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Introduce the BitCtz() function.

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* Use a WEBP_HAVE_SLOW_CLZ_CTZ flag when they are slow (LUT-based).

Change-Id: If707c121b8800438be404594a39bb123ef25b0f0
This commit is contained in:
Ilya Kurdyukov 2021-02-16 14:30:26 +07:00 committed by Skal
parent fee642870e
commit 5bd2704e30
1 changed files with 11 additions and 2 deletions
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13
src/utils/utils.h
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@ -114,17 +114,26 @@ static WEBP_INLINE void PutLE32(uint8_t* const data, uint32_t val) {
static WEBP_INLINE int BitsLog2Floor(uint32_t n) { static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
return 31 ^ __builtin_clz(n); return 31 ^ __builtin_clz(n);
} }
// counts the number of trailing zero
static WEBP_INLINE int BitsCtz(uint32_t n) { return __builtin_ctz(n); }
#elif defined(_MSC_VER) && _MSC_VER > 1310 && \ #elif defined(_MSC_VER) && _MSC_VER > 1310 && \
(defined(_M_X64) || defined(_M_IX86)) (defined(_M_X64) || defined(_M_IX86))
#include <intrin.h> #include <intrin.h>
#pragma intrinsic(_BitScanReverse) #pragma intrinsic(_BitScanReverse)
#pragma intrinsic(_BitScanForward)
static WEBP_INLINE int BitsLog2Floor(uint32_t n) { static WEBP_INLINE int BitsLog2Floor(uint32_t n) {
unsigned long first_set_bit; unsigned long first_set_bit; // NOLINT (runtime/int)
_BitScanReverse(&first_set_bit, n); _BitScanReverse(&first_set_bit, n);
return first_set_bit; return first_set_bit;
} }
#else // default: use the C-version. static WEBP_INLINE int BitsCtz(uint32_t n) {
unsigned long first_set_bit; // NOLINT (runtime/int)
_BitScanForward(&first_set_bit, n);
return first_set_bit;
}
#else // default: use the (slow) C-version.
#define WEBP_HAVE_SLOW_CLZ_CTZ // signal that the Clz/Ctz function are slow
// Returns 31 ^ clz(n) = log2(n). This is the default C-implementation, either // Returns 31 ^ clz(n) = log2(n). This is the default C-implementation, either
// based on table or not. Can be used as fallback if clz() is not available. // based on table or not. Can be used as fallback if clz() is not available.
#define WEBP_NEED_LOG_TABLE_8BIT #define WEBP_NEED_LOG_TABLE_8BIT