diff --git a/.github/workflows/benchmark.yml b/.github/workflows/benchmark.yml
index da49db8..7f39fb4 100644
--- a/.github/workflows/benchmark.yml
+++ b/.github/workflows/benchmark.yml
@@ -10,9 +10,12 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-      - uses: actions/setup-node@v1
+      - name: Setup Node.js
+        uses: actions/setup-node@v1
+        with:
+          node-version: 15
       - run: npm ci
-      - run: npm run asbuild:untouched
+      - run: npm run asbuild
       # Run benchmark with `go test -bench` and stores the output to a file
       - name: Run benchmark
         run: npm run benchmark | tee benchmark/output.txt
diff --git a/asconfig.json b/asconfig.json
index 384cc2b..af1b1b3 100644
--- a/asconfig.json
+++ b/asconfig.json
@@ -9,11 +9,11 @@
     "release": {
       "binaryFile": "build/optimized.wasm",
       "textFile": "build/optimized.wat",
-      "sourceMap": true,
+      "sourceMap": false,
       "optimizeLevel": 3,
-      "shrinkLevel": 1,
-      "converge": false,
-      "noAssert": false
+      "shrinkLevel": 0,
+      "converge": true,
+      "noAssert": true
     },
     "test": {
       "debug": true
diff --git a/assembly/__spec_tests__/generated.spec.ts b/assembly/__spec_tests__/generated.spec.ts
index 95c6422..0989a34 100644
--- a/assembly/__spec_tests__/generated.spec.ts
+++ b/assembly/__spec_tests__/generated.spec.ts
@@ -776,7 +776,11 @@ it("line: 152 - matches ([\\da-f:]+)$ against 'abc'", () => {
   expect(match.matches[0]).toBe("abc".substring(0, 3));
   expect(match.matches[1]).toBe("abc".substring(0, 3));
 });
-xit("line: 153 - aspect [Actual]: <Match>null vs [Expected]: Not <Match>null issue", () => {});
+it("line: 153 - matches ([\\da-f:]+)$ against 'fed'", () => {
+  const match = exec("([\\da-f:]+)$", "fed", "is");
+  expect(match.matches[0]).toBe("fed".substring(0, 3));
+  expect(match.matches[1]).toBe("fed".substring(0, 3));
+});
 it("line: 154 - matches ([\\da-f:]+)$ against 'E'", () => {
   const match = exec("([\\da-f:]+)$", "E", "is");
   expect(match.matches[0]).toBe("E".substring(0, 1));
@@ -1044,8 +1048,8 @@ xit("line: 199 - non capturing groups not supported", () => {});
 xit("line: 200 - non capturing groups not supported", () => {});
 xit("line: 201 - non capturing groups not supported", () => {});
 xit("line: 202 - non capturing groups not supported", () => {});
-xit("line: 203 - aspect [Actual]: <Match>null vs [Expected]: Not <Match>null issue", () => {});
-xit("line: 204 - aspect [Actual]: <Match>null vs [Expected]: Not <Match>null issue", () => {});
+xit("line: 203 - test appears to be incorrect?", () => {});
+xit("line: 204 - test appears to be incorrect?", () => {});
 it("line: 205 - matches ^   a\\ b[c ]d       $ against 'abcd'", () => {
   expectNotMatch("^   a\\ b[c ]d       $", ["abcd"]);
 });
@@ -1352,7 +1356,7 @@ it("line: 1083 - matches ^[ab]{1,3}(ab*?|b) against 'The quick brown fox'", () =
 xit("line: 1084 - back references are not supported", () => {});
 xit("line: 1085 - back references are not supported", () => {});
 xit("line: 1086 - test encoding issue", () => {});
-xit("line: 1087 - requires triage", () => {});
+xit("line: 1087 - test requires a substring function", () => {});
 xit("line: 1088 - requires triage", () => {});
 it("line: 1089 - matches abc\\x0def\\x00pqr\\x000xyz\\x0000AB against 'abc456 abc\x0def\x00pqr\x000xyz\x0000ABCDE'", () => {
   const match = exec(
@@ -1506,8 +1510,13 @@ it("line: 1144 - matches ^[W-c]+$ against 'WXY_^abc'", () => {
   const match = exec("^[W-c]+$", "WXY_^abc", "s");
   expect(match.matches[0]).toBe("WXY_^abc".substring(0, 8));
 });
-xit("line: 1145 - as-pect test issue", () => {});
-xit("line: 1146 - as-pect test issue", () => {});
+it("line: 1145 - matches ^[W-c]+$ against 'wxy'", () => {
+  expectNotMatch("^[W-c]+$", ["wxy"]);
+});
+it("line: 1146 - matches ^[W-c]+$ against 'WXY_^abc'", () => {
+  const match = exec("^[W-c]+$", "WXY_^abc", "is");
+  expect(match.matches[0]).toBe("WXY_^abc".substring(0, 8));
+});
 xit("line: 1147 - requires triage", () => {});
 xit("line: 1148 - requires triage", () => {});
 xit("line: 1149 - requires triage", () => {});
diff --git a/assembly/__tests__/character-sets.spec.ts b/assembly/__tests__/character-sets.spec.ts
index 47f5955..aeb7cf1 100644
--- a/assembly/__tests__/character-sets.spec.ts
+++ b/assembly/__tests__/character-sets.spec.ts
@@ -43,3 +43,12 @@ it("treats - as a literal in negated sets", () => {
   expectNotMatch("[^-abc]", ["-", "a", "b", "c"]);
   expectMatch("[^-abc]", ["1", "A"]);
 });
+
+it("supports case insensitive matching", () => {
+  // simple ranges
+  expectMatch("[a-c]", ["A", "C", "a", "c"], "i");
+  expectNotMatch("[a-c]", ["D", "d"], "i");
+  // complex
+  expectMatch("[W-c]", ["W", "w", "C", "c"], "i");
+  expectNotMatch("[W-c]", ["V", "v", "D", "d"], "i");
+});
diff --git a/assembly/__tests__/utils.ts b/assembly/__tests__/utils.ts
index 224daee..d264a23 100644
--- a/assembly/__tests__/utils.ts
+++ b/assembly/__tests__/utils.ts
@@ -1,7 +1,11 @@
 import { RegExp, Match } from "..";
 
-export function expectMatch(regex: string, arr: string[]): void {
-  let regexp = new RegExp(regex);
+export function expectMatch(
+  regex: string,
+  arr: string[],
+  flags: string = ""
+): void {
+  let regexp = new RegExp(regex, flags);
   for (let i = 0; i < arr.length; i++) {
     const value = arr[i];
     const match = exec(regexp, value);
@@ -9,8 +13,12 @@ export function expectMatch(regex: string, arr: string[]): void {
   }
 }
 
-export function expectNotMatch(regex: string, arr: string[]): void {
-  let regexp = new RegExp(regex);
+export function expectNotMatch(
+  regex: string,
+  arr: string[],
+  flags: string = ""
+): void {
+  let regexp = new RegExp(regex, flags);
   for (let i = 0; i < arr.length; i++) {
     const match = regexp.exec(arr[i]);
     expect(match).toBeNull(
diff --git a/assembly/nfa/matcher.ts b/assembly/nfa/matcher.ts
index a392601..b739bc4 100644
--- a/assembly/nfa/matcher.ts
+++ b/assembly/nfa/matcher.ts
@@ -8,6 +8,7 @@ import {
   NodeType,
 } from "../parser/node";
 import { Flags } from "../regexp";
+import { Range } from "../util";
 
 const enum MatcherType {
   Character,
@@ -36,7 +37,10 @@ export class Matcher {
     node: CharacterRangeNode,
     flags: Flags
   ): CharacterRangeMatcher {
-    return new CharacterRangeMatcher(node.from, node.to, flags.ignoreCase);
+    return new CharacterRangeMatcher(
+      new Range(node.from, node.to),
+      flags.ignoreCase
+    );
   }
 
   static fromCharacterSetNode(
@@ -89,20 +93,36 @@ export class CharacterMatcher extends Matcher {
   }
 }
 
+const LOWERCASE_LETTERS = new Range(Char.a, Char.z);
+const UPPERCASE_LETTERS = new Range(Char.A, Char.Z);
+const UPPER_LOWER_OFFSET = Char.a - Char.A;
+
 export class CharacterRangeMatcher extends Matcher {
-  constructor(private from: u32, private to: u32, private ignoreCase: bool) {
+  private ranges: Range[];
+
+  constructor(private range: Range, ignoreCase: bool) {
     super(MatcherType.CharacterRange);
+    this.ranges = [range];
+
     if (ignoreCase) {
-      this.from |= 0x20;
-      this.to |= 0x20;
+      const lowerIntersect = range.intersection(LOWERCASE_LETTERS);
+      if (lowerIntersect) {
+        this.ranges.push(lowerIntersect.offset(-UPPER_LOWER_OFFSET));
+      }
+      const upperIntersect = range.intersection(UPPERCASE_LETTERS);
+      if (upperIntersect) {
+        this.ranges.push(upperIntersect.offset(UPPER_LOWER_OFFSET));
+      }
     }
   }
 
   matches(code: u32): bool {
-    if (this.ignoreCase) {
-      code |= 0x20;
+    for (let i = 0, len = this.ranges.length; i < len; i++) {
+      if (code >= u32(this.ranges[i].from) && code <= u32(this.ranges[i].to)) {
+        return true;
+      }
     }
-    return code >= this.from && code <= this.to;
+    return false;
   }
 }
 
diff --git a/assembly/util.ts b/assembly/util.ts
index 8796260..9215e04 100644
--- a/assembly/util.ts
+++ b/assembly/util.ts
@@ -11,3 +11,17 @@ export function replaceAtIndex<T>(arr: T[], index: u32, item: T): T[] {
   unchecked((res[index] = item));
   return res;
 }
+
+export class Range {
+  constructor(public from: i32, public to: i32) {}
+
+  intersection(other: Range): Range | null {
+    const lower = i32(Math.max(this.from, other.from));
+    const upper = i32(Math.min(this.to, other.to));
+    return lower < upper ? new Range(lower, upper) : null;
+  }
+
+  offset(value: i32): Range {
+    return new Range(this.from + value, this.to + value);
+  }
+}
diff --git a/benchmark/benchmark.js b/benchmark/benchmark.js
index 73c58fb..3808d28 100644
--- a/benchmark/benchmark.js
+++ b/benchmark/benchmark.js
@@ -5,17 +5,14 @@ const loader = require("@assemblyscript/loader");
 const Benchmark = require("benchmark");
 const suite = new Benchmark.Suite();
 
-wasmModule = loader.instantiateSync(
-  fs.readFileSync("./build/debug/assemblyscript-regex.wasm"),
-  {
-    env: {
-      log: () => {
-        const { __getString } = wasmModule.exports;
-        console.log(__getString(strPtr));
-      },
+wasmModule = loader.instantiateSync(fs.readFileSync("./build/optimized.wasm"), {
+  env: {
+    log: () => {
+      const { __getString } = wasmModule.exports;
+      console.log(__getString(strPtr));
     },
-  }
-);
+  },
+});
 
 // the executeRegExp exported function is ex
 function executeRegex(regexStr, valueStr, untilNull = false) {
diff --git a/package-lock.json b/package-lock.json
index b577051..912869d 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -14,7 +14,6 @@
         "@types/node": "^14.14.13",
         "@typescript-eslint/eslint-plugin": "^4.14.1",
         "@typescript-eslint/parser": "^4.14.1",
-        "asbuild": "0.0.10",
         "assemblyscript": "^0.18.0",
         "benchmark": "^2.1.4",
         "eslint": "^7.18.0",
@@ -30,17 +29,13 @@
       "version": "6.0.0",
       "resolved": "https://registry.npmjs.org/@as-pect/assembly/-/assembly-6.0.0.tgz",
       "integrity": "sha512-B1bBMg2onl+RomWLlsWfrHdB8d4Xu7GOJn5eMwI4gjXvDKfbNXeSrL1gdkL7oZAHCf04XJ0XRWdUXfPdqTZdGA==",
-      "dev": true,
-      "peerDependencies": {
-        "assemblyscript": "^0.18.7"
-      }
+      "dev": true
     },
     "node_modules/@as-pect/cli": {
       "version": "6.0.0",
       "resolved": "https://registry.npmjs.org/@as-pect/cli/-/cli-6.0.0.tgz",
       "integrity": "sha512-YlRP56oflSwal03VXG/e08Ov8RsTvSYRajXh8Bb3HTLJaaoQhoodgHkQJPTZQy1rhIvJvYRN1uqZkZdppB8M/A==",
       "dev": true,
-      "license": "MIT",
       "dependencies": {
         "@as-pect/assembly": "^6.0.0",
         "@as-pect/core": "^6.0.0",
@@ -56,9 +51,6 @@
       "optionalDependencies": {
         "@as-pect/csv-reporter": "^6.0.0",
         "@as-pect/json-reporter": "^6.0.0"
-      },
-      "peerDependencies": {
-        "assemblyscript": "^0.18.7"
       }
     },
     "node_modules/@as-pect/core": {
@@ -71,9 +63,6 @@
         "@as-pect/snapshots": "^6.0.0",
         "chalk": "^4.1.0",
         "long": "^4.0.0"
-      },
-      "peerDependencies": {
-        "assemblyscript": "^0.18.7"
       }
     },
     "node_modules/@as-pect/csv-reporter": {
@@ -335,19 +324,13 @@
       "dev": true,
       "dependencies": {
         "@octokit/types": "^6.8.0"
-      },
-      "peerDependencies": {
-        "@octokit/core": ">=2"
       }
     },
     "node_modules/@octokit/plugin-request-log": {
       "version": "1.0.3",
       "resolved": "https://registry.npmjs.org/@octokit/plugin-request-log/-/plugin-request-log-1.0.3.tgz",
       "integrity": "sha512-4RFU4li238jMJAzLgAwkBAw+4Loile5haQMQr+uhFq27BmyJXcXSKvoQKqh0agsZEiUlW6iSv3FAgvmGkur7OQ==",
-      "dev": true,
-      "peerDependencies": {
-        "@octokit/core": ">=3"
-      }
+      "dev": true
     },
     "node_modules/@octokit/plugin-rest-endpoint-methods": {
       "version": "4.10.1",
@@ -357,9 +340,6 @@
       "dependencies": {
         "@octokit/types": "^6.8.2",
         "deprecation": "^2.3.1"
-      },
-      "peerDependencies": {
-        "@octokit/core": ">=3"
       }
     },
     "node_modules/@octokit/request": {
@@ -427,9 +407,6 @@
       },
       "engines": {
         "node": ">=10.18"
-      },
-      "peerDependencies": {
-        "semantic-release": ">=16.0.0 <18.0.0"
       }
     },
     "node_modules/@semantic-release/error": {
@@ -463,9 +440,6 @@
       },
       "engines": {
         "node": ">=10.18"
-      },
-      "peerDependencies": {
-        "semantic-release": ">=16.0.0 <18.0.0"
       }
     },
     "node_modules/@semantic-release/npm": {
@@ -490,9 +464,6 @@
       },
       "engines": {
         "node": ">=10.19"
-      },
-      "peerDependencies": {
-        "semantic-release": ">=16.0.0 <18.0.0"
       }
     },
     "node_modules/@semantic-release/release-notes-generator": {
@@ -514,9 +485,6 @@
       },
       "engines": {
         "node": ">=10.18"
-      },
-      "peerDependencies": {
-        "semantic-release": ">=15.8.0 <18.0.0"
       }
     },
     "node_modules/@semantic-release/release-notes-generator/node_modules/get-stream": {
@@ -529,9 +497,6 @@
       },
       "engines": {
         "node": ">=8"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/@tootallnate/once": {
@@ -758,9 +723,6 @@
       },
       "engines": {
         "node": ">=8"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/ansi-regex": {
@@ -835,20 +797,6 @@
         "node": ">=0.10.0"
       }
     },
-    "node_modules/asbuild": {
-      "version": "0.0.10",
-      "resolved": "https://registry.npmjs.org/asbuild/-/asbuild-0.0.10.tgz",
-      "integrity": "sha512-pSBYULxYuOjFVfcyeMgnJLsFbFbwqONxn9yYwMj7F44HcdVvsJzDx7wdg49uG8KmIuiQc7vjoMg3bg6oC/Al7g==",
-      "dev": true,
-      "dependencies": {
-        "yargs": "^15.4.1"
-      },
-      "bin": {
-        "asb": "bin/asb",
-        "asbuild": "bin/asb",
-        "assemblyscript-build": "bin/asb"
-      }
-    },
     "node_modules/assemblyscript": {
       "version": "0.18.9",
       "resolved": "https://registry.npmjs.org/assemblyscript/-/assemblyscript-0.18.9.tgz",
@@ -861,10 +809,6 @@
       "bin": {
         "asc": "bin/asc",
         "asinit": "bin/asinit"
-      },
-      "funding": {
-        "type": "opencollective",
-        "url": "https://opencollective.com/assemblyscript"
       }
     },
     "node_modules/astral-regex": {
@@ -980,9 +924,6 @@
       },
       "engines": {
         "node": ">=8"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/cardinal": {
@@ -1101,17 +1042,6 @@
         "node": ">=4"
       }
     },
-    "node_modules/cliui": {
-      "version": "6.0.0",
-      "resolved": "https://registry.npmjs.org/cliui/-/cliui-6.0.0.tgz",
-      "integrity": "sha512-t6wbgtoCXvAzst7QgXxJYqPt0usEfbgQdftEPbLL/cvv6HPE5VgvqCuAIDR0NgU52ds6rFwqrgakNLrHEjCbrQ==",
-      "dev": true,
-      "dependencies": {
-        "string-width": "^4.2.0",
-        "strip-ansi": "^6.0.0",
-        "wrap-ansi": "^6.2.0"
-      }
-    },
     "node_modules/color-convert": {
       "version": "2.0.1",
       "resolved": "https://registry.npmjs.org/color-convert/-/color-convert-2.0.1.tgz",
@@ -1373,9 +1303,6 @@
       },
       "engines": {
         "node": ">=10"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/del/node_modules/p-map": {
@@ -1388,9 +1315,6 @@
       },
       "engines": {
         "node": ">=10"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/deprecation": {
@@ -1517,9 +1441,6 @@
       },
       "engines": {
         "node": ">=10"
-      },
-      "funding": {
-        "url": "https://github.com/sindresorhus/execa?sponsor=1"
       }
     },
     "node_modules/env-ci/node_modules/get-stream": {
@@ -1532,9 +1453,6 @@
       },
       "engines": {
         "node": ">=8"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/env-ci/node_modules/human-signals": {
@@ -1853,9 +1771,6 @@
       },
       "engines": {
         "node": ">=10"
-      },
-      "funding": {
-        "url": "https://github.com/sindresorhus/execa?sponsor=1"
       }
     },
     "node_modules/fast-deep-equal": {
@@ -1912,9 +1827,6 @@
       },
       "engines": {
         "node": ">=8"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/file-entry-cache": {
@@ -2044,9 +1956,6 @@
       "dev": true,
       "engines": {
         "node": ">=10"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/git-log-parser": {
@@ -2447,9 +2356,6 @@
       "dev": true,
       "dependencies": {
         "has": "^1.0.3"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/ljharb"
       }
     },
     "node_modules/is-extglob": {
@@ -2651,9 +2557,6 @@
       "dependencies": {
         "graceful-fs": "^4.1.6",
         "universalify": "^2.0.0"
-      },
-      "optionalDependencies": {
-        "graceful-fs": "^4.1.6"
       }
     },
     "node_modules/jsonparse": {
@@ -2841,9 +2744,6 @@
         "cli-table": "^0.3.1",
         "node-emoji": "^1.10.0",
         "supports-hyperlinks": "^2.1.0"
-      },
-      "peerDependencies": {
-        "marked": ">=0.4.0 <2.0.0"
       }
     },
     "node_modules/meow": {
@@ -2866,9 +2766,6 @@
       },
       "engines": {
         "node": ">=10"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/meow/node_modules/type-fest": {
@@ -2878,9 +2775,6 @@
       "dev": true,
       "engines": {
         "node": ">=10"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/meow/node_modules/yargs-parser": {
@@ -3025,10 +2919,6 @@
         "nearley-test": "bin/nearley-test.js",
         "nearley-unparse": "bin/nearley-unparse.js",
         "nearleyc": "bin/nearleyc.js"
-      },
-      "funding": {
-        "type": "individual",
-        "url": "https://nearley.js.org/#give-to-nearley"
       }
     },
     "node_modules/neo-async": {
@@ -3083,9 +2973,6 @@
       "dev": true,
       "engines": {
         "node": ">=10"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/npm": {
@@ -3093,6 +2980,7 @@
       "resolved": "https://registry.npmjs.org/npm/-/npm-6.14.11.tgz",
       "integrity": "sha512-1Zh7LjuIoEhIyjkBflSSGzfjuPQwDlghNloppjruOH5bmj9midT9qcNT0tRUZRR04shU9ekrxNy9+UTBrqeBpQ==",
       "bundleDependencies": [
+        "JSONStream",
         "abbrev",
         "ansicolors",
         "ansistyles",
@@ -3133,7 +3021,6 @@
         "init-package-json",
         "is-cidr",
         "json-parse-better-errors",
-        "JSONStream",
         "lazy-property",
         "libcipm",
         "libnpm",
@@ -3184,11 +3071,11 @@
         "qrcode-terminal",
         "query-string",
         "qw",
+        "read",
         "read-cmd-shim",
         "read-installed",
         "read-package-json",
         "read-package-tree",
-        "read",
         "readable-stream",
         "readdir-scoped-modules",
         "request",
@@ -8611,9 +8498,6 @@
       },
       "engines": {
         "node": ">=6"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/opencollective-postinstall": {
@@ -8632,9 +8516,6 @@
       "dev": true,
       "engines": {
         "node": ">=8"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/p-filter": {
@@ -9039,9 +8920,6 @@
       },
       "engines": {
         "node": ">=8"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/read-pkg-up/node_modules/type-fest": {
@@ -9165,12 +9043,6 @@
         "node": ">=0.10.0"
       }
     },
-    "node_modules/require-main-filename": {
-      "version": "2.0.0",
-      "resolved": "https://registry.npmjs.org/require-main-filename/-/require-main-filename-2.0.0.tgz",
-      "integrity": "sha512-NKN5kMDylKuldxYLSUfrbo5Tuzh4hd+2E8NPPX02mZtn1VuREQToYe/ZdlJy+J3uCpfaiGF05e7B8W0iXbQHmg==",
-      "dev": true
-    },
     "node_modules/resolve": {
       "version": "1.19.0",
       "resolved": "https://registry.npmjs.org/resolve/-/resolve-1.19.0.tgz",
@@ -9179,9 +9051,6 @@
       "dependencies": {
         "is-core-module": "^2.1.0",
         "path-parse": "^1.0.6"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/ljharb"
       }
     },
     "node_modules/resolve-from": {
@@ -9310,9 +9179,6 @@
       },
       "engines": {
         "node": ">=10"
-      },
-      "funding": {
-        "url": "https://github.com/chalk/wrap-ansi?sponsor=1"
       }
     },
     "node_modules/semantic-release/node_modules/y18n": {
@@ -9402,12 +9268,6 @@
         "node": ">=8"
       }
     },
-    "node_modules/set-blocking": {
-      "version": "2.0.0",
-      "resolved": "https://registry.npmjs.org/set-blocking/-/set-blocking-2.0.0.tgz",
-      "integrity": "sha1-BF+XgtARrppoA93TgrJDkrPYkPc=",
-      "dev": true
-    },
     "node_modules/shebang-command": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/shebang-command/-/shebang-command-2.0.0.tgz",
@@ -9805,9 +9665,6 @@
       },
       "engines": {
         "node": ">=10"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/tempy/node_modules/type-fest": {
@@ -9817,9 +9674,6 @@
       "dev": true,
       "engines": {
         "node": ">=10"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/text-encoding": {
@@ -9965,9 +9819,6 @@
       "dev": true,
       "engines": {
         "node": ">=8"
-      },
-      "funding": {
-        "url": "https://github.com/sponsors/sindresorhus"
       }
     },
     "node_modules/typescript": {
@@ -10075,12 +9926,6 @@
         "node": ">= 8"
       }
     },
-    "node_modules/which-module": {
-      "version": "2.0.0",
-      "resolved": "https://registry.npmjs.org/which-module/-/which-module-2.0.0.tgz",
-      "integrity": "sha1-2e8H3Od7mQK4o6j6SzHD4/fm6Ho=",
-      "dev": true
-    },
     "node_modules/which-pm-runs": {
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/which-pm-runs/-/which-pm-runs-1.0.0.tgz",
@@ -10102,20 +9947,6 @@
       "integrity": "sha1-J1hIEIkUVqQXHI0CJkQa3pDLyus=",
       "dev": true
     },
-    "node_modules/wrap-ansi": {
-      "version": "6.2.0",
-      "resolved": "https://registry.npmjs.org/wrap-ansi/-/wrap-ansi-6.2.0.tgz",
-      "integrity": "sha512-r6lPcBGxZXlIcymEu7InxDMhdW0KDxpLgoFLcguasxCaJ/SOIZwINatK9KY/tf+ZrlywOKU0UDj3ATXUBfxJXA==",
-      "dev": true,
-      "dependencies": {
-        "ansi-styles": "^4.0.0",
-        "string-width": "^4.1.0",
-        "strip-ansi": "^6.0.0"
-      },
-      "engines": {
-        "node": ">=8"
-      }
-    },
     "node_modules/wrappy": {
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/wrappy/-/wrappy-1.0.2.tgz",
@@ -10131,12 +9962,6 @@
         "node": ">=0.4"
       }
     },
-    "node_modules/y18n": {
-      "version": "4.0.1",
-      "resolved": "https://registry.npmjs.org/y18n/-/y18n-4.0.1.tgz",
-      "integrity": "sha512-wNcy4NvjMYL8gogWWYAO7ZFWFfHcbdbE57tZO8e4cbpj8tfUcwrwqSl3ad8HxpYWCdXcJUCeKKZS62Av1affwQ==",
-      "dev": true
-    },
     "node_modules/yallist": {
       "version": "4.0.0",
       "resolved": "https://registry.npmjs.org/yallist/-/yallist-4.0.0.tgz",
@@ -10152,41 +9977,6 @@
         "node": ">= 6"
       }
     },
-    "node_modules/yargs": {
-      "version": "15.4.1",
-      "resolved": "https://registry.npmjs.org/yargs/-/yargs-15.4.1.tgz",
-      "integrity": "sha512-aePbxDmcYW++PaqBsJ+HYUFwCdv4LVvdnhBy78E57PIor8/OVvhMrADFFEDh8DHDFRv/O9i3lPhsENjO7QX0+A==",
-      "dev": true,
-      "dependencies": {
-        "cliui": "^6.0.0",
-        "decamelize": "^1.2.0",
-        "find-up": "^4.1.0",
-        "get-caller-file": "^2.0.1",
-        "require-directory": "^2.1.1",
-        "require-main-filename": "^2.0.0",
-        "set-blocking": "^2.0.0",
-        "string-width": "^4.2.0",
-        "which-module": "^2.0.0",
-        "y18n": "^4.0.0",
-        "yargs-parser": "^18.1.2"
-      },
-      "engines": {
-        "node": ">=8"
-      }
-    },
-    "node_modules/yargs-parser": {
-      "version": "18.1.3",
-      "resolved": "https://registry.npmjs.org/yargs-parser/-/yargs-parser-18.1.3.tgz",
-      "integrity": "sha512-o50j0JeToy/4K6OZcaQmW6lyXXKhq7csREXcDwk2omFPJEwUNOVtJKvmDr9EI1fAJZUyZcRF7kxGBWmRXudrCQ==",
-      "dev": true,
-      "dependencies": {
-        "camelcase": "^5.0.0",
-        "decamelize": "^1.2.0"
-      },
-      "engines": {
-        "node": ">=6"
-      }
-    },
     "node_modules/yn": {
       "version": "3.1.1",
       "resolved": "https://registry.npmjs.org/yn/-/yn-3.1.1.tgz",
@@ -10211,8 +10001,7 @@
       "version": "6.0.0",
       "resolved": "https://registry.npmjs.org/@as-pect/assembly/-/assembly-6.0.0.tgz",
       "integrity": "sha512-B1bBMg2onl+RomWLlsWfrHdB8d4Xu7GOJn5eMwI4gjXvDKfbNXeSrL1gdkL7oZAHCf04XJ0XRWdUXfPdqTZdGA==",
-      "dev": true,
-      "requires": {}
+      "dev": true
     },
     "@as-pect/cli": {
       "version": "6.0.0",
@@ -10479,8 +10268,7 @@
       "version": "1.0.3",
       "resolved": "https://registry.npmjs.org/@octokit/plugin-request-log/-/plugin-request-log-1.0.3.tgz",
       "integrity": "sha512-4RFU4li238jMJAzLgAwkBAw+4Loile5haQMQr+uhFq27BmyJXcXSKvoQKqh0agsZEiUlW6iSv3FAgvmGkur7OQ==",
-      "dev": true,
-      "requires": {}
+      "dev": true
     },
     "@octokit/plugin-rest-endpoint-methods": {
       "version": "4.10.1",
@@ -10880,15 +10668,6 @@
       "integrity": "sha1-iYUI2iIm84DfkEcoRWhJwVAaSw0=",
       "dev": true
     },
-    "asbuild": {
-      "version": "0.0.10",
-      "resolved": "https://registry.npmjs.org/asbuild/-/asbuild-0.0.10.tgz",
-      "integrity": "sha512-pSBYULxYuOjFVfcyeMgnJLsFbFbwqONxn9yYwMj7F44HcdVvsJzDx7wdg49uG8KmIuiQc7vjoMg3bg6oC/Al7g==",
-      "dev": true,
-      "requires": {
-        "yargs": "^15.4.1"
-      }
-    },
     "assemblyscript": {
       "version": "0.18.9",
       "resolved": "https://registry.npmjs.org/assemblyscript/-/assemblyscript-0.18.9.tgz",
@@ -11087,17 +10866,6 @@
         }
       }
     },
-    "cliui": {
-      "version": "6.0.0",
-      "resolved": "https://registry.npmjs.org/cliui/-/cliui-6.0.0.tgz",
-      "integrity": "sha512-t6wbgtoCXvAzst7QgXxJYqPt0usEfbgQdftEPbLL/cvv6HPE5VgvqCuAIDR0NgU52ds6rFwqrgakNLrHEjCbrQ==",
-      "dev": true,
-      "requires": {
-        "string-width": "^4.2.0",
-        "strip-ansi": "^6.0.0",
-        "wrap-ansi": "^6.2.0"
-      }
-    },
     "color-convert": {
       "version": "2.0.1",
       "resolved": "https://registry.npmjs.org/color-convert/-/color-convert-2.0.1.tgz",
@@ -17499,12 +17267,6 @@
       "integrity": "sha512-Xf0nWe6RseziFMu+Ap9biiUbmplq6S9/p+7w7YXP/JBHhrUDDUhwa+vANyubuqfZWTveU//DYVGsDG7RKL/vEw==",
       "dev": true
     },
-    "require-main-filename": {
-      "version": "2.0.0",
-      "resolved": "https://registry.npmjs.org/require-main-filename/-/require-main-filename-2.0.0.tgz",
-      "integrity": "sha512-NKN5kMDylKuldxYLSUfrbo5Tuzh4hd+2E8NPPX02mZtn1VuREQToYe/ZdlJy+J3uCpfaiGF05e7B8W0iXbQHmg==",
-      "dev": true
-    },
     "resolve": {
       "version": "1.19.0",
       "resolved": "https://registry.npmjs.org/resolve/-/resolve-1.19.0.tgz",
@@ -17685,12 +17447,6 @@
       "integrity": "sha512-bXWyL6EAKOJa81XG1OZ/Yyuq+oT0b2YLlxx7c+mrdYPaPbnj6WgVULXhinMIeZGufuUBu/eVRqXEhiv4imfwxA==",
       "dev": true
     },
-    "set-blocking": {
-      "version": "2.0.0",
-      "resolved": "https://registry.npmjs.org/set-blocking/-/set-blocking-2.0.0.tgz",
-      "integrity": "sha1-BF+XgtARrppoA93TgrJDkrPYkPc=",
-      "dev": true
-    },
     "shebang-command": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/shebang-command/-/shebang-command-2.0.0.tgz",
@@ -18231,12 +17987,6 @@
         "isexe": "^2.0.0"
       }
     },
-    "which-module": {
-      "version": "2.0.0",
-      "resolved": "https://registry.npmjs.org/which-module/-/which-module-2.0.0.tgz",
-      "integrity": "sha1-2e8H3Od7mQK4o6j6SzHD4/fm6Ho=",
-      "dev": true
-    },
     "which-pm-runs": {
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/which-pm-runs/-/which-pm-runs-1.0.0.tgz",
@@ -18255,17 +18005,6 @@
       "integrity": "sha1-J1hIEIkUVqQXHI0CJkQa3pDLyus=",
       "dev": true
     },
-    "wrap-ansi": {
-      "version": "6.2.0",
-      "resolved": "https://registry.npmjs.org/wrap-ansi/-/wrap-ansi-6.2.0.tgz",
-      "integrity": "sha512-r6lPcBGxZXlIcymEu7InxDMhdW0KDxpLgoFLcguasxCaJ/SOIZwINatK9KY/tf+ZrlywOKU0UDj3ATXUBfxJXA==",
-      "dev": true,
-      "requires": {
-        "ansi-styles": "^4.0.0",
-        "string-width": "^4.1.0",
-        "strip-ansi": "^6.0.0"
-      }
-    },
     "wrappy": {
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/wrappy/-/wrappy-1.0.2.tgz",
@@ -18278,12 +18017,6 @@
       "integrity": "sha512-LKYU1iAXJXUgAXn9URjiu+MWhyUXHsvfp7mcuYm9dSUKK0/CjtrUwFAxD82/mCWbtLsGjFIad0wIsod4zrTAEQ==",
       "dev": true
     },
-    "y18n": {
-      "version": "4.0.1",
-      "resolved": "https://registry.npmjs.org/y18n/-/y18n-4.0.1.tgz",
-      "integrity": "sha512-wNcy4NvjMYL8gogWWYAO7ZFWFfHcbdbE57tZO8e4cbpj8tfUcwrwqSl3ad8HxpYWCdXcJUCeKKZS62Av1affwQ==",
-      "dev": true
-    },
     "yallist": {
       "version": "4.0.0",
       "resolved": "https://registry.npmjs.org/yallist/-/yallist-4.0.0.tgz",
@@ -18296,35 +18029,6 @@
       "integrity": "sha512-yr2icI4glYaNG+KWONODapy2/jDdMSDnrONSjblABjD9B4Z5LgiircSt8m8sRZFNi08kG9Sm0uSHtEmP3zaEGg==",
       "dev": true
     },
-    "yargs": {
-      "version": "15.4.1",
-      "resolved": "https://registry.npmjs.org/yargs/-/yargs-15.4.1.tgz",
-      "integrity": "sha512-aePbxDmcYW++PaqBsJ+HYUFwCdv4LVvdnhBy78E57PIor8/OVvhMrADFFEDh8DHDFRv/O9i3lPhsENjO7QX0+A==",
-      "dev": true,
-      "requires": {
-        "cliui": "^6.0.0",
-        "decamelize": "^1.2.0",
-        "find-up": "^4.1.0",
-        "get-caller-file": "^2.0.1",
-        "require-directory": "^2.1.1",
-        "require-main-filename": "^2.0.0",
-        "set-blocking": "^2.0.0",
-        "string-width": "^4.2.0",
-        "which-module": "^2.0.0",
-        "y18n": "^4.0.0",
-        "yargs-parser": "^18.1.2"
-      }
-    },
-    "yargs-parser": {
-      "version": "18.1.3",
-      "resolved": "https://registry.npmjs.org/yargs-parser/-/yargs-parser-18.1.3.tgz",
-      "integrity": "sha512-o50j0JeToy/4K6OZcaQmW6lyXXKhq7csREXcDwk2omFPJEwUNOVtJKvmDr9EI1fAJZUyZcRF7kxGBWmRXudrCQ==",
-      "dev": true,
-      "requires": {
-        "camelcase": "^5.0.0",
-        "decamelize": "^1.2.0"
-      }
-    },
     "yn": {
       "version": "3.1.1",
       "resolved": "https://registry.npmjs.org/yn/-/yn-3.1.1.tgz",
diff --git a/package.json b/package.json
index 5132269..c73c17e 100644
--- a/package.json
+++ b/package.json
@@ -11,8 +11,8 @@
     "prettier": "prettier --check .",
     "prettier:write": "prettier --write .",
     "eslint:write": "npm run eslint -- --fix ",
-    "asbuild:untouched": "asb --target debug",
-    "asbuild:optimized": "asb",
+    "asbuild:untouched": "asc assembly/index.ts --target debug",
+    "asbuild:optimized": "asc assembly/index.ts --target release",
     "asbuild": "npm run asbuild:untouched && npm run asbuild:optimized",
     "tsrun": "ts-node ts/index.ts",
     "benchmark": "node benchmark/benchmark.js",
@@ -26,7 +26,6 @@
     "@types/node": "^14.14.13",
     "@typescript-eslint/eslint-plugin": "^4.14.1",
     "@typescript-eslint/parser": "^4.14.1",
-    "asbuild": "0.0.10",
     "assemblyscript": "^0.18.0",
     "benchmark": "^2.1.4",
     "eslint": "^7.18.0",
diff --git a/spec/test-generator.js b/spec/test-generator.js
index 3bcd45a..dfc32eb 100644
--- a/spec/test-generator.js
+++ b/spec/test-generator.js
@@ -21,8 +21,11 @@ const knownIssues = {
     1288,
   ],
   "test contains an octal escape sequence": [1102],
+  // the test results measure captured groups using character length / locations
+  // see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/length
+  // this is tricky to reproduce
+  "test requires a substring function": [1087],
   "requires triage": [
-    1087,
     1363,
     1369,
     1163,
@@ -32,15 +35,10 @@ const knownIssues = {
     1413,
     ...range(1301, 1308),
   ],
-  "as-pect test issue": [1145, 1146],
   "test indicates a malformed regex, whereas it appears OK in JS": [1189],
   "test regex contains syntax not supported in JS": [82, 1158, 281],
   "the test behaviour differs between PCRE and JS": [290],
-  "aspect [Actual]: <Match>null vs [Expected]: Not <Match>null issue": [
-    153,
-    203,
-    204,
-  ],
+  "test appears to be incorrect?": [203, 204],
 };
 
 const hasKnownIssue = (index) => {
diff --git a/ts/index.ts b/ts/index.ts
index 56f58b6..89080e1 100644
--- a/ts/index.ts
+++ b/ts/index.ts
@@ -5,10 +5,6 @@ globalAny.log = console.log;
 
 import { RegExp } from "../assembly/regexp";
 
-const regexObj = new RegExp("^(a){1,3}");
-const match = regexObj.exec("abc");
+const regexObj = new RegExp("[a-c]", "i");
+const match = regexObj.exec("A");
 console.log(JSON.stringify(match, null, 2));
-
-const regexObj2 = new RegExp("(a|b)c|a(b|c)");
-const match2 = regexObj2.exec("ab");
-console.log(JSON.stringify(match2, null, 2));