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Remove allocating containers from on_num

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Use std::string_view and std::array containers when
FMT_STATIC_THOUSANDS_SEPARATOR is defined.

This will help in the case for embedded system where even using
containers that can potentially allocate results in malloc/free and
new/delete being linked into the binary. In many embedded cases dynamic
library allocation is prohibited and even the cost of linking in these
libraries costs too high of a cost in flash size.

Resolves #1762
This commit is contained in:
Khalil Estell 2020-07-07 15:04:17 -07:00
parent f19b1a521e
commit 64973fb160
2 changed files with 17 additions and 4 deletions
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7
include/fmt/core.h
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@ -392,6 +392,13 @@ template <typename Char> class basic_string_view {
constexpr iterator begin() const { return data_; }
constexpr iterator end() const { return data_ + size_; }
constexpr iterator cbegin() const { return data_; }
constexpr iterator cend() const { return data_ + size_; }
constexpr bool empty() const { return size_ == 0; };
constexpr Char back() const { return data_[size_ - 1]; }
constexpr const Char& operator[](size_t pos) const { return data_[pos]; }
FMT_CONSTEXPR void remove_prefix(size_t n) {

14
include/fmt/format.h
View File

@ -34,6 +34,7 @@
#define FMT_FORMAT_H_
#include <algorithm>
#include <array>
#include <cerrno>
#include <cmath>
#include <cstdint>
@ -1552,13 +1553,18 @@ template <typename OutputIt, typename Char, typename UInt> struct int_writer {
enum { sep_size = 1 };
void on_num() {
#if !defined(FMT_STATIC_THOUSANDS_SEPARATOR)
std::string groups = grouping<Char>(locale);
#else
constexpr const char kDefaultGroups[] = "\03";
basic_string_view<Char> groups(kDefaultGroups, sizeof(kDefaultGroups));
#endif
if (groups.empty()) return on_dec();
auto sep = thousands_sep<Char>(locale);
if (!sep) return on_dec();
int num_digits = count_digits(abs_value);
int size = num_digits, n = num_digits;
std::string::const_iterator group = groups.cbegin();
auto group = groups.cbegin();
while (group != groups.cend() && num_digits > *group && *group > 0 &&
*group != max_value<char>()) {
size += sep_size;
@ -1568,9 +1574,9 @@ template <typename OutputIt, typename Char, typename UInt> struct int_writer {
if (group == groups.cend()) size += sep_size * ((n - 1) / groups.back());
char digits[40];
format_decimal(digits, abs_value, num_digits);
basic_memory_buffer<Char> buffer;
// TODO(kammce): remove the * 2!
std::array<Char, inline_buffer_size * 2> buffer;
size += prefix_size;
buffer.resize(size);
basic_string_view<Char> s(&sep, sep_size);
// Index of a decimal digit with the least significant digit having index 0.
int digit_index = 0;
@ -1590,7 +1596,7 @@ template <typename OutputIt, typename Char, typename UInt> struct int_writer {
make_checked(p, s.size()));
}
if (prefix_size != 0) p[-1] = static_cast<Char>('-');
write(out, basic_string_view<Char>(buffer.data(), buffer.size()), specs);
write(out, basic_string_view<Char>(buffer.data(), size), specs);
}
void on_chr() { *out++ = static_cast<Char>(abs_value); }