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magic division use __umulhi() #19

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asroy merged 1 commit into from
Aug 23, 2021
Merged

magic division use __umulhi() #19

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25 changes: 3 additions & 22 deletions composable_kernel/include/utility/magic_division.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -114,40 +114,21 @@ struct MagicDivision
__host__ __device__ static constexpr uint32_t
DoMagicDivision(uint32_t dividend, uint32_t multiplier, uint32_t shift)
{
uint32_t tmp = (uint64_t(dividend) * uint64_t(multiplier)) >> 32;
uint32_t tmp = __umulhi(dividend, multiplier);
return (tmp + dividend) >> shift;
}

#if 1 // debug
// HACK: magic division for int32_t
// magic division for int32_t
// HACK: use dividend_i32 as if it's uint32_t, dividend_i32 need to be
// non-negative for result to be correct
// TODO: figure out how to do magic number divison for int32_t as dividended
__host__ __device__ static constexpr int32_t
DoMagicDivision(int32_t dividend_i32, uint32_t multiplier, uint32_t shift)
{
uint32_t dividend_u32 = as_type<uint32_t>(dividend_i32);
uint32_t tmp =
(static_cast<uint64_t>(dividend_u32) * static_cast<uint64_t>(multiplier)) >> 32;
uint32_t tmp = __umulhi(dividend_u32, multiplier);
return (tmp + dividend_u32) >> shift;
}
#else
// the inline ASM is producing wrong result
__host__ __device__ static int32_t
DoMagicDivision(int32_t dividend_i32, uint32_t multiplier, uint32_t shift)
{
uint32_t r;
asm volatile("\n \
v_mul_hi_u32 %0, %1, %2 \n \
v_add_u32_e32 %0, %1, %0 \n \
v_lshrrev_b32_e32 %0, %3, %0 \n \
"
: "=v"(r)
: "v"(as_type<uint32_t>(dividend_i32)), "s"(multiplier), "s"(shift));

return as_type<int32_t>(r);
}
#endif
};

} // namespace ck
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