coffee/fast_float
1
0
Fork 0
mirror of https://github.com/fastfloat/fast_float.git synced 2025-12-07 01:06:48 +08:00
Code Issues Packages Projects Releases Wiki Activity

This uses the template trick to ensure we get only one definition

Browse Source
This commit is contained in:
Daniel Lemire 2021-04-07 13:34:53 -04:00
parent d601bd4a26
commit a8d49f40f0
2 changed files with 13 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
include/fast_float/decimal_to_binary.h
View File

@ -20,18 +20,18 @@ namespace fast_float {
template <int bit_precision>
fastfloat_really_inline
value128 compute_product_approximation(int64_t q, uint64_t w) {
const int index = 2 * int(q - smallest_power_of_five);
const int index = 2 * int(q - powers::smallest_power_of_five);
// For small values of q, e.g., q in [0,27], the answer is always exact because
// The line value128 firstproduct = full_multiplication(w, power_of_five_128[index]);
// gives the exact answer.
value128 firstproduct = full_multiplication(w, power_of_five_128[index]);
value128 firstproduct = full_multiplication(w, powers::power_of_five_128[index]);
static_assert((bit_precision >= 0) && (bit_precision <= 64), " precision should be in (0,64]");
constexpr uint64_t precision_mask = (bit_precision < 64) ?
(uint64_t(0xFFFFFFFFFFFFFFFF) >> bit_precision)
: uint64_t(0xFFFFFFFFFFFFFFFF);
if((firstproduct.high & precision_mask) == precision_mask) { // could further guard with (lower + w < lower)
// regarding the second product, we only need secondproduct.high, but our expectation is that the compiler will optimize this extra work away if needed.
value128 secondproduct = full_multiplication(w, power_of_five_128[index + 1]);
value128 secondproduct = full_multiplication(w, powers::power_of_five_128[index + 1]);
firstproduct.low += secondproduct.high;
if(secondproduct.high > firstproduct.low) {
firstproduct.high++;
@ -83,7 +83,7 @@ adjusted_mantissa compute_float(int64_t q, uint64_t w) noexcept {
answer.mantissa = 0;
return answer;
}
// At this point in time q is in [smallest_power_of_five, largest_power_of_five].
// At this point in time q is in [powers::smallest_power_of_five, powers::largest_power_of_five].
// We want the most significant bit of i to be 1. Shift if needed.
int lz = leading_zeroes(w);

12
include/fast_float/fast_table.h
View File

@ -28,10 +28,14 @@ namespace fast_float {
* infinite in binary64 so we never need to worry about powers
* of 5 greater than 308.
*/
constexpr int smallest_power_of_five = -342;
constexpr int largest_power_of_five = 308;
template <class unused = void>
struct powers_template {
constexpr static int smallest_power_of_five = binary_format<double>::smallest_power_of_ten();
constexpr static int largest_power_of_five = binary_format<double>::largest_power_of_ten();
constexpr static int number_of_entries = 2 * (largest_power_of_five - smallest_power_of_five + 1);
// Powers of five from 5^-342 all the way to 5^308 rounded toward one.
const uint64_t power_of_five_128[]= {
constexpr static uint64_t power_of_five_128[number_of_entries] = {
0xeef453d6923bd65a,0x113faa2906a13b3f,
0x9558b4661b6565f8,0x4ac7ca59a424c507,
0xbaaee17fa23ebf76,0x5d79bcf00d2df649,
@ -683,6 +687,8 @@ const uint64_t power_of_five_128[]= {
0xb6472e511c81471d,0xe0133fe4adf8e952,
0xe3d8f9e563a198e5,0x58180fddd97723a6,
0x8e679c2f5e44ff8f,0x570f09eaa7ea7648,};
};
using powers = powers_template<>;
}