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Implement exponential notation

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This commit is contained in:
Victor Zverovich 2018-08-29 10:07:29 -07:00
parent dd8c5ce442
commit 1489d3b7fa
3 changed files with 110 additions and 62 deletions
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159
include/fmt/format-inl.h
View File

@ -454,31 +454,6 @@ 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.
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++ = static_cast<char>('0' + exp / 100);
exp %= 100;
const char *d = data::DIGITS + exp * 2;
*buffer++ = d[0];
*buffer++ = d[1];
} else if (exp >= 10) {
const char *d = data::DIGITS + exp * 2;
*buffer++ = d[0];
*buffer++ = d[1];
} else {
*buffer++ = static_cast<char>('0' + exp);
}
return buffer;
}
// Generates output using Grisu2 digit-gen algorithm.
FMT_FUNC void grisu2_gen_digits(
const fp &scaled_value, const fp &scaled_upper, uint64_t delta,
@ -557,13 +532,66 @@ FMT_FUNC void grisu2_format_positive(double value, char *buffer, size_t &size,
grisu2_gen_digits(scaled_value, scaled_upper, delta, buffer, size, dec_exp);
}
FMT_FUNC void round(char *buffer, size_t &size, int &exp,
int digits_to_remove) {
size -= to_unsigned(digits_to_remove);
exp += digits_to_remove;
int digit = buffer[size] - '0';
// TODO: proper rounding and carry
if (digit > 5 || (digit == 5 && (digits_to_remove > 1 ||
(buffer[size - 1] - '0') % 2) != 0)) {
++buffer[size - 1];
}
}
// 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++ = static_cast<char>('0' + exp / 100);
exp %= 100;
const char *d = data::DIGITS + exp * 2;
*buffer++ = d[0];
*buffer++ = d[1];
} else {
const char *d = data::DIGITS + exp * 2;
*buffer++ = d[0];
*buffer++ = d[1];
}
return buffer;
}
FMT_FUNC void format_exp_notation(
char *buffer, size_t &size, int exp, int precision, bool upper) {
// Insert a decimal point after the first digit and add an exponent.
std::memmove(buffer + 2, buffer + 1, size - 1);
buffer[1] = '.';
exp += static_cast<int>(size) - 1;
int num_digits = precision - static_cast<int>(size) + 1;
if (num_digits > 0) {
std::uninitialized_fill_n(buffer + size + 1, num_digits, '0');
size += to_unsigned(num_digits);
} else if (num_digits < 0) {
round(buffer, size, exp, -num_digits);
}
char *p = buffer + size + 1;
*p++ = upper ? 'E' : 'e';
size = to_unsigned(write_exponent(p, exp) - buffer);
}
// 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,
int precision) {
int precision, bool upper) {
// pow(10, full_exp - 1) <= v <= pow(10, full_exp).
int full_exp = static_cast<int>(size) + exp;
int int_size = static_cast<int>(size);
int full_exp = int_size + exp;
const int exp_threshold = 21;
if (int_size <= full_exp && full_exp <= exp_threshold) {
// 1234e7 -> 12340000000[.0+]
@ -578,12 +606,13 @@ FMT_FUNC void grisu2_prettify(char *buffer, size_t &size, int exp,
} else if (0 < full_exp && full_exp <= exp_threshold) {
// 1234e-2 -> 12.34[0+]
int fractional_size = -exp;
std::memmove(buffer + full_exp + 1, buffer + full_exp, fractional_size);
std::memmove(buffer + full_exp + 1, buffer + full_exp,
to_unsigned(fractional_size));
buffer[full_exp] = '.';
if (fractional_size < precision) {
int num_zeros = precision - fractional_size;
int num_zeros = precision - fractional_size;
if (num_zeros > 0) {
std::uninitialized_fill_n(buffer + size + 1, num_zeros, '0');
size += num_zeros;
size += to_unsigned(num_zeros);
}
++size;
} else if (-6 < full_exp && full_exp <= 0) {
@ -595,25 +624,20 @@ FMT_FUNC void grisu2_prettify(char *buffer, size_t &size, int exp,
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);
format_exp_notation(buffer, size, exp, precision, upper);
}
}
inline void round(char *, size_t &size, int &exp, int diff) {
// TODO: round instead of truncating
size -= to_unsigned(diff);
exp += diff;
}
#if FMT_CLANG_VERSION
# define FMT_FALLTHROUGH [[clang::fallthrough]];
#else
# define FMT_FALLTHROUGH
#endif
// Formats a nonnegative 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 precision, bool write_decimal_point) {
FMT_ASSERT(value >= 0, "value is negative");
int dec_exp = 0; // K in Grisu.
if (value > 0) {
@ -625,24 +649,43 @@ FMT_FUNC void grisu2_format(double value, char *buffer, size_t &size, char type,
const int default_precision = 6;
if (precision < 0)
precision = default_precision;
if (!type || type == 'g' || type == 'G') {
int extra_digits = static_cast<int>(size) - precision;
if (extra_digits > 0)
round(buffer, size, dec_exp, extra_digits);
precision = 0;
} else if (type == 'f' || type == 'F') {
if (precision > 0)
print_decimal_point = true;
int extra_digits = -dec_exp - precision;
if (extra_digits > 0) {
if (extra_digits >= static_cast<int>(size))
extra_digits = static_cast<int>(size) - 1;
round(buffer, size, dec_exp, extra_digits);
bool upper = false;
switch (type) {
case 'G':
upper = true;
FMT_FALLTHROUGH
case '\0': case 'g': {
int digits_to_remove = static_cast<int>(size) - precision;
if (digits_to_remove > 0) {
round(buffer, size, dec_exp, digits_to_remove);
// Remove trailing zeros.
while (size > 0 && buffer[size - 1] == '0') {
--size;
++dec_exp;
}
}
precision = 0;
break;
}
if (print_decimal_point && precision < 1)
case 'F':
upper = true;
FMT_FALLTHROUGH
case 'f': {
int digits_to_remove = -dec_exp - precision;
if (digits_to_remove > 0) {
if (digits_to_remove >= static_cast<int>(size))
digits_to_remove = static_cast<int>(size) - 1;
round(buffer, size, dec_exp, digits_to_remove);
}
break;
}
case 'e': case 'E':
format_exp_notation(buffer, size, dec_exp, precision, type == 'E');
return;
}
if (write_decimal_point && precision < 1)
precision = 1;
grisu2_prettify(buffer, size, dec_exp, precision);
grisu2_prettify(buffer, size, dec_exp, precision, upper);
}
} // namespace internal

4
include/fmt/format.h
View File

@ -150,7 +150,7 @@ FMT_END_NAMESPACE
#endif
#ifndef FMT_USE_GRISU
# define FMT_USE_GRISU 1
# define FMT_USE_GRISU 0
#endif
// __builtin_clz is broken in clang with Microsoft CodeGen:
@ -282,7 +282,7 @@ inline bool use_grisu() {
// 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, char type,
int precision, bool print_decimal_point);
int precision, bool write_decimal_point);
template <typename Allocator>
typename Allocator::value_type *allocate(Allocator& alloc, std::size_t n) {

9
test/printf-test.cc
View File

@ -180,8 +180,13 @@ TEST(PrintfTest, HashFlag) {
safe_sprintf(buffer, "%#E", -42.0);
EXPECT_PRINTF(buffer, "%#E", -42.0);
EXPECT_PRINTF("-42.0000", "%#g", -42.0);
EXPECT_PRINTF("-42.0000", "%#G", -42.0);
if (fmt::internal::use_grisu()) {
EXPECT_PRINTF("-42.0", "%#g", -42.0);
EXPECT_PRINTF("-42.0", "%#G", -42.0);
} else {
EXPECT_PRINTF("-42.0000", "%#g", -42.0);
EXPECT_PRINTF("-42.0000", "%#G", -42.0);
}
safe_sprintf(buffer, "%#a", 16.0);
EXPECT_PRINTF(buffer, "%#a", 16.0);