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Optimize parse_nonnegative_int

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This commit is contained in:
Victor Zverovich 2021-06-13 19:05:31 -07:00
parent f28cf3302d
commit 3c8fad126c
1 changed files with 22 additions and 18 deletions
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36
include/fmt/core.h
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@ -8,10 +8,10 @@
#ifndef FMT_CORE_H_
#define FMT_CORE_H_
#include <climits> // INT_MAX
#include <cstdio> // std::FILE
#include <cstring>
#include <iterator>
#include <limits>
#include <string>
#include <type_traits>
@ -2103,21 +2103,25 @@ template <typename Char, typename ErrorHandler>
FMT_CONSTEXPR auto parse_nonnegative_int(const Char*& begin, const Char* end,
ErrorHandler&& eh) -> int {
FMT_ASSERT(begin != end && '0' <= *begin && *begin <= '9', "");
unsigned value = 0;
// Convert to unsigned to prevent a warning.
const unsigned max_int = to_unsigned(INT_MAX);
unsigned big = max_int / 10;
unsigned value = 0, prev = 0;
auto p = begin;
do {
// Check for overflow.
if (value > big) {
value = max_int + 1;
break;
}
value = value * 10 + unsigned(*begin - '0');
++begin;
} while (begin != end && '0' <= *begin && *begin <= '9');
if (value > max_int) eh.on_error("number is too big");
prev = value;
value = value * 10 + unsigned(*p - '0');
++p;
} while (p != end && '0' <= *p && *p <= '9');
auto num_digits = p - begin;
begin = p;
if (num_digits <= std::numeric_limits<int>::digits10)
return static_cast<int>(value);
// Check for overflow.
const unsigned big = to_unsigned((std::numeric_limits<int>::max)());
if (num_digits == std::numeric_limits<int>::digits10 + 1 &&
prev * 10ull + unsigned(p[-1] - '0') <= big) {
return static_cast<int>(value);
}
eh.on_error("number is too big");
return -1;
}
// Parses fill and alignment.
@ -2454,8 +2458,8 @@ class compile_parse_context
public:
explicit FMT_CONSTEXPR compile_parse_context(
basic_string_view<Char> format_str, int num_args = INT_MAX,
ErrorHandler eh = {})
basic_string_view<Char> format_str,
int num_args = (std::numeric_limits<int>::max)(), ErrorHandler eh = {})
: base(format_str, eh), num_args_(num_args) {}
FMT_CONSTEXPR auto next_arg_id() -> int {