On Thu, 24 May 2018, Liu Hao wrote:
在 2018/5/23 21:10, Martin Storsjö 写道:
+#if __INTRINSIC_PROLOG(_BitScanReverse)
+__MINGW_EXTENSION unsigned char _BitScanReverse(unsigned __LONG32
*Index, unsigned __LONG32 Mask);
+#if !__has_builtin(_BitScanReverse)
+__MINGW_EXTENSION __INTRINSICS_USEINLINE
+unsigned char _BitScanReverse(unsigned __LONG32 *Index, unsigned
__LONG32 Mask)
+{
+ if (Mask == 0)
+ return 0;
+ *Index = 31 - __builtin_clz(Mask);
Is hardcoding `31` here safe? The use of `__LONG32` reminds me about
the
fact that MSYS2 for x64 shares some of our headers but expects `long`
to
be 64-bit long, where `31` apparently will cause trouble.
Maybe it could be changed to
```
*Index = 31 - (__builtin_clz(Mask) - (__LONG_WIDTH__ - 32));
```
which is then equivalent to
```
*Index = __LONG_WIDTH__ - 1 - __builtin_clz(Mask);
```
?
I guess that's doable (I guess you mean __SIZEOF_LONG__ * 8?), although
I'd maybe rather use "sizeof(Mask) * 8" instead.
// Martin
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