From bd413d3d853e2c1fc0382b328176ff912d79da70 Mon Sep 17 00:00:00 2001
From: Alessandro Gatti <a.gatti@frob.it>
Date: Sun, 17 Aug 2025 07:28:35 +0200
Subject: [PATCH] py/asmthumb: Fix T3 encoding of conditional branches.

This commit fixes the encoding of conditional branch opcodes emitted for
ARMv7-M targets, when the emitter decides to use the T3 encoding for
said operation.

Fields J1 and J2 are now present in the generated opcode word, along
with correcting some minor issues in bitmasks and shifts computation.

This fixes #17940.

Signed-off-by: Alessandro Gatti <a.gatti@frob.it>
---
 py/asmthumb.c                             |  5 ++---
 tests/micropython/viper_large_jump.py     | 20 ++++++++++++++++++++
 tests/micropython/viper_large_jump.py.exp |  1 +
 3 files changed, 23 insertions(+), 3 deletions(-)
 create mode 100644 tests/micropython/viper_large_jump.py
 create mode 100644 tests/micropython/viper_large_jump.py.exp

diff --git a/py/asmthumb.c b/py/asmthumb.c
index 93860d2fdc1a2..58cc7aea88085 100644
--- a/py/asmthumb.c
+++ b/py/asmthumb.c
@@ -267,9 +267,8 @@ bool asm_thumb_b_n_label(asm_thumb_t *as, uint label) {
 
 #define OP_BCC_N(cond, byte_offset) (0xd000 | ((cond) << 8) | (((byte_offset) >> 1) & 0x00ff))
 
-// all these bit-arithmetic operations need coverage testing!
-#define OP_BCC_W_HI(cond, byte_offset) (0xf000 | ((cond) << 6) | (((byte_offset) >> 10) & 0x0400) | (((byte_offset) >> 14) & 0x003f))
-#define OP_BCC_W_LO(byte_offset) (0x8000 | ((byte_offset) & 0x2000) | (((byte_offset) >> 1) & 0x0fff))
+#define OP_BCC_W_HI(cond, byte_offset) (0xf000 | ((cond) << 6) | (((byte_offset) >> 10) & 0x0400) | (((byte_offset) >> 12) & 0x003f))
+#define OP_BCC_W_LO(byte_offset) (0x8000 | (((byte_offset) >> 5) & 0x2000) | (((byte_offset) >> 8) & 0x0800) | (((byte_offset) >> 1) & 0x07ff))
 
 bool asm_thumb_bcc_nw_label(asm_thumb_t *as, int cond, uint label, bool wide) {
     mp_uint_t dest = get_label_dest(as, label);
diff --git a/tests/micropython/viper_large_jump.py b/tests/micropython/viper_large_jump.py
new file mode 100644
index 0000000000000..1c5913dec1ea2
--- /dev/null
+++ b/tests/micropython/viper_large_jump.py
@@ -0,0 +1,20 @@
+COUNT = 600
+
+
+try:
+    code = """
+@micropython.viper
+def f() -> int:
+    x = 0
+    while x < 10:
+"""
+    for i in range(COUNT):
+        code += "        x += 1\n"
+    code += "    return x"
+    exec(code)
+except MemoryError:
+    print("SKIP-TOO-LARGE")
+    raise SystemExit
+
+
+print(f())
diff --git a/tests/micropython/viper_large_jump.py.exp b/tests/micropython/viper_large_jump.py.exp
new file mode 100644
index 0000000000000..e9f960cf4ac4e
--- /dev/null
+++ b/tests/micropython/viper_large_jump.py.exp
@@ -0,0 +1 @@
+600