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Add a function to get cached power of 10

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Victor Zverovich
2018-05-27 10:57:26 -07:00
parent 2f257b7291
commit 468c243ca8
3 changed files with 30 additions and 7 deletions
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13
include/fmt/format-inl.h
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@@ -342,6 +342,19 @@ FMT_FUNC fp operator*(fp x, fp y) {
uint64_t mid = (bd >> 32) + (ad & mask) + (bc & mask) + (1U << 31);
return fp(ac + (ad >> 32) + (bc >> 32) + (mid >> 32), x.e + y.e + 64);
}
FMT_FUNC fp get_cached_power(int min_exponent, int &pow10_exponent) {
const double one_over_log2_10 = 0.30102999566398114; // 1 / log2(10)
int index = static_cast<int>(std::ceil(
(min_exponent + fp::fp_significand_size - 1) * one_over_log2_10));
// Decimal exponent of the first (smallest) cached power of 10.
const int first_dec_exp = -348;
// Difference between two consecutive decimal exponents in cached powers of 10.
const int dec_exp_step = 8;
index = (index - first_dec_exp - 1) / dec_exp_step + 1;
pow10_exponent = first_dec_exp + index * dec_exp_step;
return fp(data::POW10_SIGNIFICANDS[index], data::POW10_EXPONENTS[index]);
}
} // namespace internal
#if FMT_USE_WINDOWS_H