From 2a952dd0b2de035f5bace42022c4879f527d174e Mon Sep 17 00:00:00 2001 From: Victor Zverovich Date: Sun, 26 Aug 2018 09:51:49 -0700 Subject: [PATCH] Implement some formatting options in Grisu --- include/fmt/format-inl.h | 81 +++++++++++++++++++++++++++++++++------- include/fmt/format.h | 13 ++++--- 2 files changed, 74 insertions(+), 20 deletions(-) diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h index cc102680..55459c06 100644 --- a/include/fmt/format-inl.h +++ b/include/fmt/format-inl.h @@ -364,12 +364,14 @@ FMT_FUNC fp get_cached_power(int min_exponent, int &pow10_exponent) { return fp(data::POW10_SIGNIFICANDS[index], data::POW10_EXPONENTS[index]); } -// Writes the exponent exp in the form "[-]d{1,3}" to buffer. +// Writes the exponent exp in the form "[+-]d{1,3}" to buffer. FMT_FUNC char *write_exponent(char *buffer, int exp) { FMT_ASSERT(-1000 < exp && exp < 1000, "exponent out of range"); if (exp < 0) { *buffer++ = '-'; exp = -exp; + } else { + *buffer++ = '+'; } if (exp >= 100) { *buffer++ = '0' + static_cast(exp / 100); @@ -446,25 +448,56 @@ FMT_FUNC void grisu2_gen_digits( // Prettifies the output of the Grisu2 algorithm. // The number is given as v = buffer * 10^exp. -FMT_FUNC void grisu2_prettify(char *buffer, size_t &size, int exp) { +FMT_FUNC void grisu2_prettify(char *buffer, size_t &size, int exp, char type, + int precision, bool print_decimal_point) { + int int_size = static_cast(size); // 10^(full_exp - 1) <= v <= 10^full_exp. - int full_exp = static_cast(size) + exp; - // Insert a decimal point after the first digit and add an exponent. - std::memmove(buffer + 2, buffer + 1, size - 1); - buffer[1] = '.'; - char *p = buffer + size + 1; - *p++ = 'e'; - size = to_unsigned(write_exponent(p, full_exp - 1) - buffer); + int full_exp = int_size + exp; + if (int_size <= full_exp && full_exp <= 21) { + // 1234e7 -> 12340000000 + char *p = std::uninitialized_fill_n( + buffer + int_size, full_exp - int_size, '0'); + if (print_decimal_point && int_size < precision) { + *p++ = '.'; + p = std::uninitialized_fill_n(p, precision - int_size, '0'); + } + size = to_unsigned(p - buffer); + } else if (0 < full_exp && full_exp <= 21) { + // 1234e-2 -> 12.34 + size_t fractional_size = int_size - full_exp; + std::memmove(buffer + full_exp + 1, buffer + full_exp, fractional_size); + buffer[full_exp] = '.'; + if (type == 'f' && fractional_size < precision) { + size_t num_zeros = precision - fractional_size; + std::uninitialized_fill_n(buffer + size + 1, num_zeros, '0'); + size += num_zeros; + } + ++size; + } else if (-6 < full_exp && full_exp <= 0) { + // 1234e-6 -> 0.001234 + int offset = 2 - full_exp; + std::memmove(buffer + offset, buffer, size); + buffer[0] = '0'; + buffer[1] = '.'; + std::uninitialized_fill_n(buffer + 2, -full_exp, '0'); + size = to_unsigned(int_size + offset); + } else { + // Insert a decimal point after the first digit and add an exponent. + std::memmove(buffer + 2, buffer + 1, size - 1); + buffer[1] = '.'; + char *p = buffer + size + 1; + *p++ = 'e'; + size = to_unsigned(write_exponent(p, full_exp - 1) - buffer); + } } -// Formats value using Grisu2 algorithm. Grisu2 doesn't give any guarantees on -// the shortness of the result. -FMT_FUNC void grisu2_format(double value, char *buffer, size_t &size) { +FMT_FUNC void grisu2_format_positive(double value, char *buffer, size_t &size, + int &dec_exp) { + FMT_ASSERT(value > 0, "value is nonpositive"); fp fp_value(value); fp lower, upper; // w^- and w^+ in the Grisu paper. fp_value.compute_boundaries(lower, upper); // Find a cached power of 10 close to 1 / upper. - int dec_exp = 0; // K in Grisu. const int min_exp = -60; // alpha in Grisu. auto dec_pow = get_cached_power( // \tilde{c}_{-k} in Grisu. min_exp - (upper.e + fp::significand_size), dec_exp); @@ -477,7 +510,27 @@ FMT_FUNC void grisu2_format(double value, char *buffer, size_t &size) { --scaled_upper.f; // \tilde{M}^+ - 1 ulp -> M^+_{\downarrow}. uint64_t delta = scaled_upper.f - scaled_lower.f; grisu2_gen_digits(scaled_value, scaled_upper, delta, buffer, size, dec_exp); - grisu2_prettify(buffer, size, dec_exp); +} + +// Formats value using Grisu2 algorithm. Grisu2 doesn't give any guarantees on +// the shortness of the result. +FMT_FUNC void grisu2_format(double value, char *buffer, size_t &size, char type, + int precision, bool print_decimal_point) { + int dec_exp = 0; // K in Grisu. + if (value != 0) { + grisu2_format_positive(value, buffer, size, dec_exp); + } else { + *buffer = '0'; + size = 1; + } + if (precision < 0) + precision = 6; + if (size > precision) { + // TODO: round instead of truncating + dec_exp += size - precision; + size = precision; + } + grisu2_prettify(buffer, size, dec_exp, type, precision, print_decimal_point); } } // namespace internal diff --git a/include/fmt/format.h b/include/fmt/format.h index 33843994..ffd0a7ed 100644 --- a/include/fmt/format.h +++ b/include/fmt/format.h @@ -367,7 +367,8 @@ FMT_API fp get_cached_power(int min_exponent, int &pow10_exponent); // Formats value using Grisu2 algorithm: // https://www.cs.tufts.edu/~nr/cs257/archive/florian-loitsch/printf.pdf -FMT_API void grisu2_format(double value, char *buffer, size_t &size); +FMT_API void grisu2_format(double value, char *buffer, size_t &size, char type, + int precision, bool print_decimal_point); template typename Allocator::value_type *allocate(Allocator& alloc, std::size_t n) { @@ -2949,12 +2950,12 @@ void basic_writer::write_double(T value, const format_specs &spec) { basic_memory_buffer buffer; if (internal::const_check(FMT_USE_GRISU && sizeof(T) <= sizeof(double) && std::numeric_limits::is_iec559)) { - // The max size = 10 (hi) + 20 (lo) + 5 (exp). - enum { BUF_SIZE = 35 }; - char buf[BUF_SIZE]; + char buf[100]; // TODO: correct buffer size size_t size = 0; - internal::grisu2_format(static_cast(value), buf, size); - FMT_ASSERT(size <= BUF_SIZE, "buffer overflow"); + internal::grisu2_format( + static_cast(value), buf, size, static_cast(spec.type()), + spec.precision(), spec.flag(HASH_FLAG)); + FMT_ASSERT(size <= 100, "buffer overflow"); buffer.append(buf, buf + size); // TODO: avoid extra copy } else { format_specs normalized_spec(spec);