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Help MSVC to not generate horrible assembly
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@jk-jeon
jk-jeon committed Feb 22, 2022
1 parent 478edcc commit fa139ad
Showing 1 changed file with 101 additions and 65 deletions.
166 changes: 101 additions & 65 deletions source/dragonbox_to_chars.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -66,48 +66,6 @@ namespace jkj::dragonbox {

JKJ_FORCEINLINE static void print_9_digits(std::uint32_t s32, int& exponent,
char*& buffer) noexcept {
std::uint64_t prod;

auto get_next_two_digits = [&]() {
prod = std::uint32_t(prod) * std::uint64_t(100);
return int(prod >> 32);
};
auto print_1_initial = [&](int digit) {
buffer[0] = char(digit + '0');
buffer[1] = '.';
buffer += 2;
};
auto print_2_initial = [&](int two_digits) {
buffer[0] = radix_100_table[two_digits * 2];
buffer[1] = '.';
buffer[2] = radix_100_table[two_digits * 2 + 1];
buffer += 3;
};
auto print_2 = [&](int two_digits) {
std::memcpy(buffer, radix_100_table + two_digits * 2, 2);
buffer += 2;
};
auto print = [&](std::uint64_t magic_number, int extra_shift, auto remaining_count) {
prod = s32 * magic_number;
prod >>= extra_shift;
auto two_digits = int(prod >> 32);

if (two_digits < 10) {
print_1_initial(two_digits);
exponent += (2 * remaining_count);
for (int i = 0; i < remaining_count; ++i) {
print_2(get_next_two_digits());
}
}
else {
print_2_initial(two_digits);
exponent += (2 * remaining_count + 1);
for (int i = 0; i < remaining_count; ++i) {
print_2(get_next_two_digits());
}
}
};

if (s32 < 100) {
if (s32 < 10) {
// 1 digit.
Expand All @@ -116,7 +74,10 @@ namespace jkj::dragonbox {
}
else {
// 2 digits.
print_2_initial(int(s32));
buffer[0] = radix_100_table[int(s32) * 2];
buffer[1] = '.';
buffer[2] = radix_100_table[int(s32) * 2 + 1];
buffer += 3;
exponent += 1;
}
}
Expand All @@ -125,31 +86,114 @@ namespace jkj::dragonbox {
if (s32 < 1'0000) {
// 3 or 4 digits.
// 42949673 = ceil(2^32 / 100)
print(42949673, 0, std::integral_constant<int, 1>{});
auto prod = s32 * std::uint64_t(42949673);
auto two_digits = int(prod >> 32);

// 3 digits.
if (two_digits < 10) {
buffer[0] = char(two_digits + '0');
buffer[1] = '.';
exponent += 2;
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 2, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 4;
}
// 4 digits.
else {
buffer[0] = radix_100_table[two_digits * 2];
buffer[1] = '.';
buffer[2] = radix_100_table[two_digits * 2 + 1];
exponent += 3;
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 3, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 5;
}
}
else {
// 5 or 6 digits.
// 429497 = ceil(2^32 / 1'0000)
print(429497, 0, std::integral_constant<int, 2>{});
auto prod = s32 * std::uint64_t(429497);
auto two_digits = int(prod >> 32);

// 5 digits.
if (two_digits < 10) {
buffer[0] = char(two_digits + '0');
buffer[1] = '.';
exponent += 4;
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 2, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 4, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 6;
}
// 6 digits.
else {
buffer[0] = radix_100_table[two_digits * 2];
buffer[1] = '.';
buffer[2] = radix_100_table[two_digits * 2 + 1];
exponent += 5;
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 3, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 5, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 7;
}
}
}
else {
if (s32 < 1'0000'0000) {
// 7 or 8 digits.
// 281474978 = ceil(2^48 / 100'0000) + 1
print(281474978, 16, std::integral_constant<int, 3>{});
auto prod = s32 * std::uint64_t(281474978);
prod >>= 16;
auto two_digits = int(prod >> 32);

// 7 digits.
if (two_digits < 10) {
buffer[0] = char(two_digits + '0');
buffer[1] = '.';
exponent += 6;
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 2, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 4, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 6, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 8;
}
// 8 digits.
else {
buffer[0] = radix_100_table[two_digits * 2];
buffer[1] = '.';
buffer[2] = radix_100_table[two_digits * 2 + 1];
exponent += 7;
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 3, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 5, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 7, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 9;
}
}
else {
// 9 digits.
// 1441151882 = ceil(2^57 / 1'0000'0000) + 1
prod = s32 * std::uint64_t(1441151882);
auto prod = s32 * std::uint64_t(1441151882);
prod >>= 25;
print_1_initial(int(prod >> 32));
buffer[0] = char(int(prod >> 32) + '0');
buffer[1] = '.';
exponent += 8;
print_2(get_next_two_digits());
print_2(get_next_two_digits());
print_2(get_next_two_digits());
print_2(get_next_two_digits());

prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 2, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 4, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 6, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
std::memcpy(buffer + 8, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 10;
}
}
}
Expand Down Expand Up @@ -209,24 +253,16 @@ namespace jkj::dragonbox {
auto prod = second_block * std::uint64_t(281474978);
prod >>= 16;
prod += 1;
auto first_two_digits = std::uint32_t(prod >> 32);
exponent += 8;

std::memcpy(buffer + 0, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
auto second_two_digits = std::uint32_t(prod >> 32);

std::memcpy(buffer + 2, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
auto third_two_digits = std::uint32_t(prod >> 32);

std::memcpy(buffer + 4, radix_100_table + int(prod >> 32) * 2, 2);
prod = std::uint32_t(prod) * std::uint64_t(100);
auto fourth_two_digits = std::uint32_t(prod >> 32);

std::memcpy(buffer + 0, &radix_100_table[first_two_digits * 2], 2);
std::memcpy(buffer + 2, &radix_100_table[second_two_digits * 2], 2);
std::memcpy(buffer + 4, &radix_100_table[third_two_digits * 2], 2);
std::memcpy(buffer + 6, &radix_100_table[fourth_two_digits * 2], 2);
std::memcpy(buffer + 6, radix_100_table + int(prod >> 32) * 2, 2);
buffer += 8;

exponent += 8;
}

// Print exponent and return
Expand Down

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