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libobs/util: Fix undefined behavior and optimize util_mul64_64

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Shifting an integer larger than its bit width can have undefined
behavior.  This not only fixes that issue, but also optimizes the
shift functions.
This commit is contained in:
jp9000 2018-09-07 17:25:49 -07:00
parent 85d259e05c
commit e8eec22d15
1 changed files with 14 additions and 6 deletions
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20
libobs/util/util_uint128.h
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@ -51,11 +51,19 @@ static inline util_uint128_t util_add128(util_uint128_t a, util_uint128_t b)
return out;
}
static inline util_uint128_t util_lshift64(uint64_t a, int num)
static inline util_uint128_t util_lshift64_internal_32(uint64_t a)
{
util_uint128_t val;
val.low = a << num;
val.high = a >> (64 - num);
val.low = a << 32;
val.high = a >> 32;
return val;
}
static inline util_uint128_t util_lshift64_internal_64(uint64_t a)
{
util_uint128_t val;
val.low = 0;
val.high = a;
return val;
}
@ -69,13 +77,13 @@ static inline util_uint128_t util_mul64_64(uint64_t a, uint64_t b)
out.high = 0;
m = (a >> 32) * (b & 0xFFFFFFFFULL);
out = util_add128(out, util_lshift64(m, 32));
out = util_add128(out, util_lshift64_internal_32(m));
m = (a & 0xFFFFFFFFULL) * (b >> 32);
out = util_add128(out, util_lshift64(m, 32));
out = util_add128(out, util_lshift64_internal_32(m));
m = (a >> 32) * (b >> 32);
out = util_add128(out, util_lshift64(m, 64));
out = util_add128(out, util_lshift64_internal_64(m));
return out;
}