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Diffstat (limited to 'src/int_math.c')
-rw-r--r-- | src/int_math.c | 70 |
1 files changed, 70 insertions, 0 deletions
diff --git a/src/int_math.c b/src/int_math.c new file mode 100644 index 00000000..b20b14a6 --- /dev/null +++ b/src/int_math.c @@ -0,0 +1,70 @@ +/* + Copyright 2019-2020 David Robillard <http://drobilla.net> + + Permission to use, copy, modify, and/or distribute this software for any + purpose with or without fee is hereby granted, provided that the above + copyright notice and this permission notice appear in all copies. + + THIS SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. +*/ + +#include "int_math.h" + +#include <assert.h> + +unsigned +serd_clz32(const uint32_t i) +{ + assert(i != 0); + +#ifdef HAVE_BUILTIN_CLZ + return (unsigned)__builtin_clz(i); +#else + unsigned n = 32u; + uint32_t bits = i; + for (unsigned s = 16; s > 0; s >>= 1) { + const uint32_t left = bits >> s; + if (left) { + n -= s; + bits = left; + } + } + return n - bits; +#endif +} + +unsigned +serd_clz64(const uint64_t i) +{ + assert(i != 0); + +#ifdef HAVE_BUILTIN_CLZLL + return (unsigned)__builtin_clzll(i); +#else + return i & 0xFFFFFFFF00000000 ? serd_clz32(i >> 32) + : 32 + serd_clz32(i & 0xFFFFFFFF); +#endif +} + +uint64_t +serd_ilog2(const uint64_t i) +{ + assert(i != 0); + return (64 - serd_clz64(i | 1)) - 1; +} + +uint64_t +serd_ilog10(const uint64_t i) +{ + // See https://graphics.stanford.edu/~seander/bithacks.html#IntegerLog10 + const uint64_t log2 = serd_ilog2(i); + const uint64_t t = (log2 + 1) * 1233 >> 12; + + return t - (i < POW10[t]) + (i == 0); +} |