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Implement __builtin_clz in MSVC #102

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Implement __builtin_clz in MSVC #102

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9 changes: 9 additions & 0 deletions src/zopfli/symbols.h
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,15 @@ Utilities for using the lz77 symbols of the deflate spec.
/* __builtin_clz available beginning with GCC 3.4 */
#elif __GNUC__ * 100 + __GNUC_MINOR__ >= 304
# define ZOPFLI_HAS_BUILTIN_CLZ
/* _BitScanReverse available beginning with Visual Studio 2005 */
#elif _MSC_VER >= 1400
# include <intrin.h>
# define ZOPFLI_HAS_BUILTIN_CLZ
static int __inline __builtin_clz(unsigned int x) {
unsigned long r;
_BitScanReverse(&r, x);
return 31 ^ r;
}
#endif

/* Gets the amount of extra bits for the given dist, cfr. the DEFLATE spec. */
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