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Use popcount.

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This commit is contained in:
Thomas Harte
2025-08-30 10:44:00 -04:00
parent 357f98f015
commit 5d2c156bc9
1 changed files with 7 additions and 17 deletions
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Processors/68000/Implementation/68000Implementation.hpp
+7 -17
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@@ -8,6 +8,7 @@
#pragma once
#include <bit>
#include <cassert>
#include <cstdio>
@@ -2916,12 +2917,6 @@ template <bool did_overflow> void ProcessorBase::did_divu(uint32_t dividend, uin
}
}
#define convert_to_bit_count_16(x) \
x = ((x & 0xaaaa) >> 1) + (x & 0x5555); \
x = ((x & 0xcccc) >> 2) + (x & 0x3333); \
x = ((x & 0xf0f0) >> 4) + (x & 0x0f0f); \
x = ((x & 0xff00) >> 8) + (x & 0x00ff);
template <bool did_overflow> void ProcessorBase::did_divs(int32_t dividend, int32_t divisor) {
// The route to spotting divide by 0 is just nn nn.
if(!divisor) {
@@ -2948,9 +2943,8 @@ template <bool did_overflow> void ProcessorBase::did_divs(int32_t dividend, int3
// undefined difference between a nop cycle an an idle wait is relevant here?
dynamic_instruction_length_ += 49;
int result_bits = ~abs(dividend / divisor) & 0xfffe;
convert_to_bit_count_16(result_bits);
dynamic_instruction_length_ += result_bits;
const auto result_bits = uint16_t(~abs(dividend / divisor) & 0xfffe);
dynamic_instruction_length_ += std::popcount(result_bits);
// Determine the tail cost; a divisor of less than 0 leads to one exit,
// a divisor of greater than zero makes the result a function of the
@@ -2969,23 +2963,19 @@ template <bool did_overflow> void ProcessorBase::did_divs(int32_t dividend, int3
}
}
template <typename IntT> void ProcessorBase::did_mulu(IntT multiplier) {
template <typename IntT> void ProcessorBase::did_mulu(const IntT multiplier) {
// Count number of bits set.
convert_to_bit_count_16(multiplier);
dynamic_instruction_length_ = 17 + multiplier;
dynamic_instruction_length_ = 17 + std::popcount(multiplier);
}
template <typename IntT> void ProcessorBase::did_muls(IntT multiplier) {
// Count number of transitions from 0 to 1 or from 1 to 0 — i.e. the
// number of times that a bit is not equal to the one to its right.
// Treat the bit to the right of b0 as 0.
int number_of_pairs = (multiplier ^ (multiplier << 1)) & 0xffff;
convert_to_bit_count_16(number_of_pairs);
dynamic_instruction_length_ = 17 + number_of_pairs;
const auto number_of_pairs = uint16_t((multiplier ^ (multiplier << 1)));
dynamic_instruction_length_ = 17 + std::popcount(number_of_pairs);
}
#undef convert_to_bit_count_16
template <typename IntT> void ProcessorBase::did_shift(int bits_shifted) {
if constexpr (sizeof(IntT) == 4) {
dynamic_instruction_length_ = bits_shifted + 2;