External/fmt
8
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Implement fallback FP formatting with given precision (#1526)

Browse Source
This commit is contained in:
Victor Zverovich 2020-09-07 09:34:05 -07:00
parent fb289cf56b
commit 9f312fe87e
2 changed files with 70 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

92
include/fmt/format-inl.h
View File

@ -984,7 +984,7 @@ struct grisu_shortest_handler {
// Floating-Point Printout ((FPP)^2) algorithm by Steele & White:
// https://fmt.dev/p372-steele.pdf.
template <typename Double>
void fallback_format(Double d, buffer<char>& buf, int& exp10) {
void fallback_format(Double d, int num_digits, buffer<char>& buf, int& exp10) {
bigint numerator; // 2 * R in (FPP)^2.
bigint denominator; // 2 * S in (FPP)^2.
// lower and upper are differences between value and corresponding boundaries.
@ -1031,34 +1031,71 @@ void fallback_format(Double d, buffer<char>& buf, int& exp10) {
upper = &upper_store;
}
}
if (!upper) upper = &lower;
// Invariant: value == (numerator / denominator) * pow(10, exp10).
bool even = (value.f & 1) == 0;
int num_digits = 0;
char* data = buf.data();
for (;;) {
int digit = numerator.divmod_assign(denominator);
bool low = compare(numerator, lower) - even < 0; // numerator <[=] lower.
// numerator + upper >[=] pow10:
bool high = add_compare(numerator, *upper, denominator) + even > 0;
data[num_digits++] = static_cast<char>('0' + digit);
if (low || high) {
if (!low) {
++data[num_digits - 1];
} else if (high) {
int result = add_compare(numerator, numerator, denominator);
// Round half to even.
if (result > 0 || (result == 0 && (digit % 2) != 0))
if (num_digits < 0) {
// Generate the shortest representation.
if (!upper) upper = &lower;
bool even = (value.f & 1) == 0;
num_digits = 0;
char* data = buf.data();
for (;;) {
int digit = numerator.divmod_assign(denominator);
bool low = compare(numerator, lower) - even < 0; // numerator <[=] lower.
// numerator + upper >[=] pow10:
bool high = add_compare(numerator, *upper, denominator) + even > 0;
data[num_digits++] = static_cast<char>('0' + digit);
if (low || high) {
if (!low) {
++data[num_digits - 1];
} else if (high) {
int result = add_compare(numerator, numerator, denominator);
// Round half to even.
if (result > 0 || (result == 0 && (digit % 2) != 0))
++data[num_digits - 1];
}
buf.try_resize(to_unsigned(num_digits));
exp10 -= num_digits - 1;
return;
}
numerator *= 10;
lower *= 10;
if (upper != &lower) *upper *= 10;
}
}
// Generate the given number of digits.
exp10 -= num_digits - 1;
if (num_digits == 0) {
buf.try_resize(1);
denominator *= 10;
buf[0] = add_compare(numerator, numerator, denominator) > 0 ? '1' : '0';
return;
}
buf.try_resize(to_unsigned(num_digits));
for (int i = 0; i < num_digits - 1; ++i) {
int digit = numerator.divmod_assign(denominator);
buf[i] = static_cast<char>('0' + digit);
numerator *= 10;
}
int digit = numerator.divmod_assign(denominator);
auto result = add_compare(numerator, numerator, denominator);
if (result > 0 || (result == 0 && (digit % 2) != 0)) {
if (digit == 9) {
const auto overflow = '0' + 10;
buf[num_digits - 1] = overflow;
// Propagate the carry.
for (int i = num_digits - 1; i > 0 && buf[i] == overflow; --i) {
buf[i] = '0';
++buf[i - 1];
}
if (buf[0] == overflow) {
buf[0] = '0';
++exp10;
}
buf.try_resize(to_unsigned(num_digits));
exp10 -= num_digits - 1;
return;
}
numerator *= 10;
lower *= 10;
if (upper != &lower) *upper *= 10;
++digit;
}
buf[num_digits - 1] = static_cast<char>('0' + digit);
}
// Formats value using the Grisu algorithm
@ -1110,7 +1147,7 @@ int format_float(T value, int precision, float_specs specs, buffer<char>& buf) {
boundaries.upper - boundaries.lower, exp, handler);
if (result == digits::error) {
exp += handler.size - cached_exp10 - 1;
fallback_format(value, buf, exp);
fallback_format(value, -1, buf, exp);
return exp;
}
buf.try_resize(to_unsigned(handler.size));
@ -1121,8 +1158,11 @@ int format_float(T value, int precision, float_specs specs, buffer<char>& buf) {
min_exp - (normalized.e + fp::significand_size), cached_exp10);
normalized = normalized * cached_pow;
fixed_handler handler{buf.data(), 0, precision, -cached_exp10, fixed};
if (grisu_gen_digits(normalized, 1, exp, handler) == digits::error)
return snprintf_float(value, precision, specs, buf);
if (grisu_gen_digits(normalized, 1, exp, handler) == digits::error) {
exp += handler.size - cached_exp10 - 1;
fallback_format(value, handler.size, buf, exp);
return exp;
}
int num_digits = handler.size;
if (!fixed && !specs.showpoint) {
// Remove trailing zeros.

6
test/format-test.cc
View File

@ -762,8 +762,7 @@ TEST(FormatterTest, HashFlag) {
EXPECT_EQ("4.e+01", format("{:#.0e}", 42.0));
EXPECT_EQ("0.", format("{:#.0f}", 0.01));
EXPECT_EQ("0.50", format("{:#.2g}", 0.5));
auto s = format("{:#.0f}", 0.5); // MSVC's printf uses wrong rounding mode.
EXPECT_TRUE(s == "0." || s == "1.");
EXPECT_EQ("0.", format("{:#.0f}", 0.5));
EXPECT_THROW_MSG(format("{0:#", 'c'), format_error,
"missing '}' in format string");
EXPECT_THROW_MSG(format("{0:#}", 'c'), format_error,
@ -1279,6 +1278,9 @@ TEST(FormatterTest, PrecisionRounding) {
char buffer[64];
safe_sprintf(buffer, "%f", n);
EXPECT_EQ(buffer, format("{:f}", n));
EXPECT_EQ("225.51575035152063720",
fmt::format("{:.17f}", 225.51575035152064));
EXPECT_EQ("-761519619559038.2", fmt::format("{:.1f}", -761519619559038.2));
}
TEST(FormatterTest, FormatNaN) {