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Avoid extra copy

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This commit is contained in:
Victor Zverovich 2018-10-17 08:19:46 -07:00
parent 98f1c1fe87
commit e8efdef8de
3 changed files with 14 additions and 15 deletions
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12
include/fmt/format-inl.h
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@ -667,14 +667,16 @@ FMT_FUNC void format_float(char *buffer, size_t &size, int exp,
template <typename Double>
FMT_FUNC typename std::enable_if<sizeof(Double) == sizeof(uint64_t), bool>::type
grisu2_format(Double value, char *buffer, size_t &size,
grisu2_specs specs) {
grisu2_format(Double value, buffer &buf, grisu2_specs specs) {
FMT_ASSERT(value >= 0, "value is negative");
char *buffer = buf.data();
if (value == 0) {
gen_digits_params params(specs, 1);
*buffer = '0';
size = 1;
size_t size = 1;
format_float(buffer, size, 0, params);
FMT_ASSERT(buf.capacity() >= size, "");
buf.resize(size);
return true;
}
@ -705,12 +707,14 @@ FMT_FUNC typename std::enable_if<sizeof(Double) == sizeof(uint64_t), bool>::type
// lo (p2 in Grisu) contains the least significants digits of scaled_upper.
// lo = supper % one.
uint64_t lo = upper.f & (one.f - 1);
size = 0;
size_t size = 0;
if (!grisu2_gen_digits(buffer, size, hi, lo, exp, delta, one, diff,
params.max_digits)) {
return false;
}
format_float(buffer, size, cached_exp + exp, params);
FMT_ASSERT(buf.capacity() >= size, "");
buf.resize(size);
return true;
}
} // namespace internal

14
include/fmt/format.h
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@ -299,10 +299,10 @@ struct grisu2_specs {
// https://www.cs.tufts.edu/~nr/cs257/archive/florian-loitsch/printf.pdf
template <typename Double>
FMT_API typename std::enable_if<sizeof(Double) == sizeof(uint64_t), bool>::type
grisu2_format(Double value, char *buffer, size_t &size, grisu2_specs);
grisu2_format(Double value, buffer &buf, grisu2_specs);
template <typename Double>
inline typename std::enable_if<sizeof(Double) != sizeof(uint64_t), bool>::type
grisu2_format(Double, char *, size_t &, grisu2_specs) { return false; }
grisu2_format(Double, buffer &, grisu2_specs) { return false; }
template <typename Allocator>
typename Allocator::value_type *allocate(Allocator& alloc, std::size_t n) {
@ -2862,22 +2862,16 @@ void basic_writer<Range>::write_double(T value, const format_specs &spec) {
bool use_grisu = internal::use_grisu() && sizeof(T) <= sizeof(double) &&
type != 'a' && type != 'A';
if (use_grisu) {
char buf[100]; // TODO: correct buffer size
size_t size = 0;
auto gs = internal::grisu2_specs();
gs.type = type;
gs.precision = spec.precision();
gs.flags = spec.flags_;
use_grisu = internal::grisu2_format(
static_cast<double>(value), buf, size, gs);
if (use_grisu) {
FMT_ASSERT(size <= 100, "buffer overflow");
buffer.append(buf, buf + size); // TODO: avoid extra copy
}
use_grisu = internal::grisu2_format(static_cast<double>(value), buffer, gs);
}
if (!use_grisu) {
format_specs normalized_spec(spec);
normalized_spec.type_ = handler.type;
buffer.clear();
write_double_sprintf(value, normalized_spec, buffer);
}
size_t n = buffer.size();

3
test/format-impl-test.cc
View File

@ -104,7 +104,8 @@ TEST(FPTest, GetCachedPower) {
TEST(FPTest, Grisu2FormatCompilesWithNonIEEEDouble) {
size_t size = 0;
grisu2_format(4.2f, FMT_NULL, size, fmt::internal::grisu2_specs());
fmt::memory_buffer buf;
grisu2_format(4.2f, buf, fmt::internal::grisu2_specs());
}
template <typename T>