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Make all float_common.h functions constexpr in C++20

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This commit is contained in:
Lenard Szolnoki 2023-03-03 22:43:52 +00:00
parent a3e00eed59
commit 52618851fd
1 changed files with 81 additions and 19 deletions
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100
include/fast_float/float_common.h
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@ -7,6 +7,25 @@
#include <cstring>
#include <type_traits>
#ifdef __has_include
#if __has_include(<version>)
#include <version>
#endif
#endif
#if __cpp_lib_bit_cast >= 201806L
#include <bit>
#define FASTFLOAT_HAS_BIT_CAST 1
#else
#define FASTFLOAT_HAS_BIT_CAST 0
#endif
#if __cpp_lib_is_constant_evaluated >= 201811L
#define FASTFLOAT_HAS_IS_CONSTANT_EVALUATED 1
#else
#define FASTFLOAT_HAS_IS_CONSTANT_EVALUATED 0
#endif
#if (defined(__x86_64) || defined(__x86_64__) || defined(_M_X64) \
|| defined(__amd64) || defined(__aarch64__) || defined(_M_ARM64) \
|| defined(__MINGW64__) \
@ -98,8 +117,25 @@
#define FASTFLOAT_CONSTEXPR14
#endif
// Testing for relevant C++20 constexpr library features
#if FASTFLOAT_HAS_IS_CONSTANT_EVALUATED \
&& FASTFLOAT_HAS_BIT_CAST \
&& __cpp_lib_constexpr_algorithms >= 201806L /*For std::copy and std::fill*/
#define FASTFLOAT_CONSTEXPR20 constexpr
#else
#define FASTFLOAT_CONSTEXPR20
#endif
namespace fast_float {
fastfloat_really_inline constexpr bool cpp20_and_in_constexpr() {
#if FASTFLOAT_HAS_IS_CONSTANT_EVALUATED
return std::is_constant_evaluated();
#else
return false;
#endif
}
// Compares two ASCII strings in a case insensitive manner.
inline FASTFLOAT_CONSTEXPR14 bool
fastfloat_strncasecmp(const char *input1, const char *input2, size_t length) {
@ -139,9 +175,27 @@ struct value128 {
constexpr value128() : low(0), high(0) {}
};
/* Helper C++11 constexpr generic implementation of leading_zeroes */
fastfloat_really_inline constexpr
int leading_zeroes_generic(uint64_t input_num, int last_bit = 0) {
return (
((input_num & uint64_t(0xffffffff00000000)) && (input_num >>= 32, last_bit |= 32)),
((input_num & uint64_t( 0xffff0000)) && (input_num >>= 16, last_bit |= 16)),
((input_num & uint64_t( 0xff00)) && (input_num >>= 8, last_bit |= 8)),
((input_num & uint64_t( 0xf0)) && (input_num >>= 4, last_bit |= 4)),
((input_num & uint64_t( 0xc)) && (input_num >>= 2, last_bit |= 2)),
((input_num & uint64_t( 0x2)) && (input_num >>= 1, last_bit |= 1)),
63 - last_bit
);
}
/* result might be undefined when input_num is zero */
fastfloat_really_inline int leading_zeroes(uint64_t input_num) {
fastfloat_really_inline FASTFLOAT_CONSTEXPR20
int leading_zeroes(uint64_t input_num) {
assert(input_num > 0);
if (cpp20_and_in_constexpr()) {
return leading_zeroes_generic(input_num);
}
#ifdef FASTFLOAT_VISUAL_STUDIO
#if defined(_M_X64) || defined(_M_ARM64)
unsigned long leading_zero = 0;
@ -150,31 +204,20 @@ fastfloat_really_inline int leading_zeroes(uint64_t input_num) {
_BitScanReverse64(&leading_zero, input_num);
return (int)(63 - leading_zero);
#else
int last_bit = 0;
if(input_num & uint64_t(0xffffffff00000000)) input_num >>= 32, last_bit |= 32;
if(input_num & uint64_t( 0xffff0000)) input_num >>= 16, last_bit |= 16;
if(input_num & uint64_t( 0xff00)) input_num >>= 8, last_bit |= 8;
if(input_num & uint64_t( 0xf0)) input_num >>= 4, last_bit |= 4;
if(input_num & uint64_t( 0xc)) input_num >>= 2, last_bit |= 2;
if(input_num & uint64_t( 0x2)) input_num >>= 1, last_bit |= 1;
return 63 - last_bit;
return leading_zeroes_generic(input_num);
#endif
#else
return __builtin_clzll(input_num);
#endif
}
#ifdef FASTFLOAT_32BIT
// slow emulation routine for 32-bit
fastfloat_really_inline constexpr uint64_t emulu(uint32_t x, uint32_t y) {
return x * (uint64_t)y;
}
// slow emulation routine for 32-bit
#if !defined(__MINGW64__)
fastfloat_really_inline constexpr uint64_t _umul128(uint64_t ab, uint64_t cd,
uint64_t *hi) {
fastfloat_really_inline FASTFLOAT_CONSTEXPR14
uint64_t umul128_generic(uint64_t ab, uint64_t cd, uint64_t *hi) {
uint64_t ad = emulu((uint32_t)(ab >> 32), (uint32_t)cd);
uint64_t bd = emulu((uint32_t)ab, (uint32_t)cd);
uint64_t adbc = ad + emulu((uint32_t)ab, (uint32_t)(cd >> 32));
@ -184,14 +227,28 @@ fastfloat_really_inline constexpr uint64_t _umul128(uint64_t ab, uint64_t cd,
(adbc_carry << 32) + !!(lo < bd);
return lo;
}
#ifdef FASTFLOAT_32BIT
// slow emulation routine for 32-bit
#if !defined(__MINGW64__)
fastfloat_really_inline FASTFLOAT_CONSTEXPR14
uint64_t _umul128(uint64_t ab, uint64_t cd, uint64_t *hi) {
return umul128_generic(ab, cd, hi);
}
#endif // !__MINGW64__
#endif // FASTFLOAT_32BIT
// compute 64-bit a*b
fastfloat_really_inline value128 full_multiplication(uint64_t a,
uint64_t b) {
fastfloat_really_inline FASTFLOAT_CONSTEXPR20
value128 full_multiplication(uint64_t a, uint64_t b) {
if (cpp20_and_in_constexpr()) {
value128 answer;
answer.low = umul128_generic(a, b, &answer.high);
return answer;
}
value128 answer;
#if defined(_M_ARM64) && !defined(__MINGW32__)
// ARM64 has native support for 64-bit multiplications, no need to emulate
@ -205,7 +262,7 @@ fastfloat_really_inline value128 full_multiplication(uint64_t a,
answer.low = uint64_t(r);
answer.high = uint64_t(r >> 64);
#else
#error Not implemented
answer.low = umul128_generic(a, b, &answer.high);
#endif
return answer;
}
@ -442,12 +499,17 @@ template <> inline constexpr binary_format<double>::equiv_uint
}
template<typename T>
fastfloat_really_inline void to_float(bool negative, adjusted_mantissa am, T &value) {
fastfloat_really_inline FASTFLOAT_CONSTEXPR20
void to_float(bool negative, adjusted_mantissa am, T &value) {
using uint = typename binary_format<T>::equiv_uint;
uint word = (uint)am.mantissa;
word |= uint(am.power2) << binary_format<T>::mantissa_explicit_bits();
word |= uint(negative) << binary_format<T>::sign_index();
#if FASTFLOAT_HAS_BIT_CAST
value = std::bit_cast<T>(word);
#else
::memcpy(&value, &word, sizeof(T));
#endif
}
#if FASTFLOAT_SKIP_WHITE_SPACE // disabled by default