While shifting "value" to left, we would iterate through all bits
of an unsigned long long, while we only expect to count through
"size * CHAR_BIT" bits; instead shift bits to the right and just
count the trailing zeros.
This fixes fate with MSVC.
---
Fixed the UB by shifting to the right instead of to the left.
---
compat/stdbit/stdbit.h | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/compat/stdbit/stdbit.h b/compat/stdbit/stdbit.h
index b434fc2357..53419cf9f9 100644
--- a/compat/stdbit/stdbit.h
+++ b/compat/stdbit/stdbit.h
@@ -178,11 +178,14 @@ static inline unsigned int
stdc_trailing_zeros_uc(unsigned char value)
static inline unsigned int __stdc_trailing_zeros(unsigned long long value,
unsigned int size)
{
- unsigned int zeros = size * CHAR_BIT;
+ unsigned int zeros = 0;
- while (value != 0) {
- value <<= 1;
- zeros--;
+ if (!value)
+ return size * CHAR_BIT;
+
+ while ((value & 1) == 0) {
+ value >>= 1;
+ zeros++;
}
return zeros;
--
2.39.5 (Apple Git-154)
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