Minor tweak on number parsing (simdjson#1041)

lemire · web-flow · commit 534632dc52f3 · 2020-07-17T12:14:10.000-04:00
* Tweak.
diff --git a/src/generic/stage2/numberparsing.h b/src/generic/stage2/numberparsing.h
@@ -437,17 +437,13 @@ really_inline bool parse_number(const uint8_t *const src, W &writer) {
   int longest_digit_count = negative ? 19 : 20;
   if (digit_count > longest_digit_count) { return INVALID_NUMBER(src); }
   if (digit_count == longest_digit_count) {
-    // Anything negative above INT64_MAX is either invalid or INT64_MIN.
-    if (negative && i > uint64_t(INT64_MAX)) {
-      // If the number is negative and can't fit in a signed integer, it's invalid.
-      if (i > uint64_t(INT64_MAX)+1) { return INVALID_NUMBER(src); }
-
-      // If it's negative, it has to be INT64_MAX+1 now (or INT64_MIN).
-      // C++ can't reliably negate uint64_t INT64_MIN, it seems. Special case it.
-      WRITE_INTEGER(INT64_MIN, src, writer);
+    if(negative) {
+      // Anything negative above INT64_MAX+1 is invalid
+      if (i > uint64_t(INT64_MAX)+1) {
+        return INVALID_NUMBER(src); 
+      }
+      WRITE_INTEGER(~i+1, src, writer);
       return is_structural_or_whitespace(*p);
-    }
-
     // Positive overflow check:
     // - A 20 digit number starting with 2-9 is overflow, because 18,446,744,073,709,551,615 is the
     //   biggest uint64_t.
@@ -460,14 +456,14 @@ really_inline bool parse_number(const uint8_t *const src, W &writer) {
     // - Therefore, if the number is positive and lower than that, it's overflow.
     // - The value we are looking at is less than or equal to 9,223,372,036,854,775,808 (INT64_MAX).
     //
-    if (!negative && (src[0] != uint8_t('1') || i <= uint64_t(INT64_MAX))) { return INVALID_NUMBER(src); }
+    }  else if (src[0] != uint8_t('1') || i <= uint64_t(INT64_MAX)) { return INVALID_NUMBER(src); }
   }
 
   // Write unsigned if it doesn't fit in a signed integer.
   if (i > uint64_t(INT64_MAX)) {
     WRITE_UNSIGNED(i, src, writer);
   } else {
-    WRITE_INTEGER(negative ? 0 - i : i, src, writer);
+    WRITE_INTEGER(negative ? (~i+1) : i, src, writer);
   }
   return is_structural_or_whitespace(*p);
 }
