diff options
Diffstat (limited to 'prism/internal/bit.h')
| -rw-r--r-- | prism/internal/bit.h | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/prism/internal/bit.h b/prism/internal/bit.h new file mode 100644 index 0000000000..b0111a4c2c --- /dev/null +++ b/prism/internal/bit.h @@ -0,0 +1,42 @@ +#ifndef PRISM_INTERNAL_BIT_H +#define PRISM_INTERNAL_BIT_H + +#include "prism/compiler/inline.h" + +/* + * Count trailing zero bits in a 64-bit value. Used by SWAR identifier scanning + * to find the first non-matching byte in a word. + * + * Precondition: v must be nonzero. The result is undefined when v == 0 + * (matching the behavior of __builtin_ctzll and _BitScanForward64). + */ +#if defined(__GNUC__) || defined(__clang__) +#define pm_ctzll(v) ((unsigned) __builtin_ctzll(v)) +#elif defined(_MSC_VER) +#include <intrin.h> +#include <stdint.h> + +static PRISM_INLINE unsigned +pm_ctzll(uint64_t v) { + unsigned long index; + _BitScanForward64(&index, v); + return (unsigned) index; +} +#else +#include <stdint.h> + +static PRISM_INLINE unsigned +pm_ctzll(uint64_t v) { + unsigned c = 0; + v &= (uint64_t) (-(int64_t) v); + if (v & 0x00000000FFFFFFFFULL) c += 0; else c += 32; + if (v & 0x0000FFFF0000FFFFULL) c += 0; else c += 16; + if (v & 0x00FF00FF00FF00FFULL) c += 0; else c += 8; + if (v & 0x0F0F0F0F0F0F0F0FULL) c += 0; else c += 4; + if (v & 0x3333333333333333ULL) c += 0; else c += 2; + if (v & 0x5555555555555555ULL) c += 0; else c += 1; + return c; +} +#endif + +#endif |