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Always "mix" hash values in case poor hash values are provided.

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greg
2019-04-05 21:12:24 -04:00
parent 6a720b4d0c
commit 7cc2644fba
3 changed files with 187 additions and 108 deletions
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parallel_hashmap/phmap_bits.h
Vendored
+2 -23
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@@ -474,6 +474,7 @@ PHMAP_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero32(uint32_t n) {
*high = static_cast<uint64_t>(result >> 64);
return static_cast<uint64_t>(result);
}
#define PHMAP_HAS_UMUL128 1
#elif (defined(_MSC_VER))
#if defined(_WIN64)
#pragma intrinsic(_umul128)
@@ -481,29 +482,7 @@ PHMAP_BASE_INTERNAL_FORCEINLINE int CountTrailingZerosNonZero32(uint32_t n) {
{
return _umul128(a, b, high);
}
#else
#pragma intrinsic(__emulu)
inline uint64_t umul128(uint64_t multiplier, uint64_t multiplicand, uint64_t *product_hi)
{
uint64_t a = multiplier >> 32;
uint64_t b = (uint32_t)multiplier; // & 0xFFFFFFFF;
uint64_t c = multiplicand >> 32;
uint64_t d = (uint32_t)multiplicand; // & 0xFFFFFFFF;
uint64_t ad = __emulu(a, d);
uint64_t bd = __emulu(b, d);
uint64_t adbc = ad + __emulu(b, c);
uint64_t adbc_carry = (adbc < ad); // ? 1 : 0;
// MSVC gets confused by the ternary and makes worse code than using a boolean in an integer context for 1 : 0
// multiplier * multiplicand = product_hi * 2^64 + product_lo
uint64_t product_lo = bd + (adbc << 32);
uint64_t product_lo_carry = (product_lo < bd); // ? 1 : 0;
*product_hi = __emulu(a, c) + (adbc >> 32) + (adbc_carry << 32) + product_lo_carry;
return product_lo;
}
#define PHMAP_HAS_UMUL128 1
#endif
#endif