Fix ScanReverse on posix/32-bit.

The use of the __builtin_clz intrinsic and the associated math were incorrect. Bug: angleproject:5736 Change-Id: I9627c7fc179c0e1bffeecaee39f7a88d9c62d079 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2845232 Commit-Queue: Yuly Novikov <ynovikov@chromium.org> Reviewed-by: Yuly Novikov <ynovikov@chromium.org>

Fix ScanReverse on posix/32-bit.
e0e5eb84 · Jamie Madill · Commit Bot · e167d453 · e0e5eb84
Commit e0e5eb84 authored Apr 21, 2021 by Jamie Madill Committed by Commit Bot Apr 22, 2021
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Showing with 9 additions and 4 deletions

mathutil.h src/common/mathutil.h +9 -4

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--- a/src/common/mathutil.h
+++ b/src/common/mathutil.h
@@ -1194,10 +1194,15 @@ inline unsigned long ScanReverse(uint64_t bits)
 #    if defined(ANGLE_IS_64_BIT_CPU)
    return static_cast<unsigned long>(sizeof(uint64_t) * CHAR_BIT - 1 - __builtin_clzll(bits));
 #    else
-    int tempResult = static_cast<uint32_t>(bits >> 32) == 0
+    if (static_cast<uint32_t>(bits >> 32) == 0)
-                         ? __builtin_clzll(static_cast<int32_t>(bits))
+    {
-                         : (__builtin_clzll(static_cast<int32_t>(bits >> 32)) + 32);
+        return sizeof(uint32_t) * CHAR_BIT - 1 - __builtin_clz(static_cast<uint32_t>(bits));
-    return static_cast<unsigned long>(sizeof(uint64_t) * CHAR_BIT - 1 - tempResult);
+    }
+    else
+    {
+        return sizeof(uint32_t) * CHAR_BIT - 1 - __builtin_clz(static_cast<uint32_t>(bits >> 32)) +
+               32;
+    }
 #    endif  // defined(ANGLE_IS_64_BIT_CPU)
 }
 #endif  // defined(ANGLE_PLATFORM_POSIX)