diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h index c8a2e3a9..ee2f83de 100644 --- a/include/fmt/format-inl.h +++ b/include/fmt/format-inl.h @@ -461,19 +461,30 @@ FMT_FUNC fp get_cached_power(int min_exponent, int &pow10_exponent) { return fp(data::POW10_SIGNIFICANDS[index], data::POW10_EXPONENTS[index]); } +FMT_FUNC void grisu2_round(char *buffer, size_t size, uint64_t delta, + uint64_t remainder, uint64_t exp, uint64_t diff) { + while (remainder < diff && delta - remainder >= exp && + (remainder + exp < diff || diff - remainder > remainder + exp - diff)) { + --buffer[size - 1]; + remainder += exp; + } +} + // Generates output using Grisu2 digit-gen algorithm. FMT_FUNC void grisu2_gen_digits( const fp &scaled_value, const fp &scaled_upper, uint64_t delta, char *buffer, size_t &size, int &dec_exp) { internal::fp one(1ull << -scaled_upper.e, scaled_upper.e); + internal::fp diff = scaled_upper - scaled_value; // wp_w in Grisu. // hi (p1 in Grisu) contains the most significant digits of scaled_upper. // hi = floor(scaled_upper / one). uint32_t hi = static_cast(scaled_upper.f >> -one.e); // lo (p2 in Grisu) contains the least significants digits of scaled_upper. - // lo = scaled_upper mod 1. + // lo = scaled_upper % one. uint64_t lo = scaled_upper.f & (one.f - 1); size = 0; auto exp = count_digits(hi); // kappa in Grisu. + // Generate digits for the most significant part (hi). while (exp > 0) { uint32_t digit = 0; // This optimization by miloyip reduces the number of integer divisions by @@ -498,11 +509,13 @@ FMT_FUNC void grisu2_gen_digits( uint64_t remainder = (static_cast(hi) << -one.e) + lo; if (remainder <= delta) { dec_exp += exp; - // TODO: use scaled_value - (void)scaled_value; + grisu2_round(buffer, size, delta, remainder, + static_cast(data::POWERS_OF_10_32[exp]) << -one.e, + diff.f); return; } } + // Generate digits for the least significant part (lo). for (;;) { lo *= 10; delta *= 10; @@ -513,6 +526,8 @@ FMT_FUNC void grisu2_gen_digits( --exp; if (lo < delta) { dec_exp += exp; + grisu2_round(buffer, size, delta, lo, one.f, + diff.f * data::POWERS_OF_10_32[-exp]); return; } } @@ -552,7 +567,7 @@ FMT_FUNC void round(char *buffer, size_t &size, int &exp, } } -// Writes the exponent exp in the form "[+-]d{1,3}" to buffer. +// Writes the exponent exp in the form "[+-]d{2,3}" to buffer. FMT_FUNC char *write_exponent(char *buffer, int exp) { FMT_ASSERT(-1000 < exp && exp < 1000, "exponent out of range"); if (exp < 0) {