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// Copyright 2021 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/time/time_delta_from_string.h"
#include <limits>
#include <utility>
#include "base/strings/string_util.h"
#include "base/time/time.h"
namespace base {
namespace {
// Strips the |expected| prefix from the start of the given string, returning
// |true| if the strip operation succeeded or false otherwise.
//
// Example:
//
// StringPiece input("abc");
// EXPECT_TRUE(ConsumePrefix(input, "a"));
// EXPECT_EQ(input, "bc");
//
// Adapted from absl::ConsumePrefix():
// https://cs.chromium.org/chromium/src/third_party/abseil-cpp/absl/strings/strip.h?l=45&rcl=2c22e9135f107a4319582ae52e2e3e6b201b6b7c
bool ConsumePrefix(StringPiece& str, StringPiece expected) {
if (!StartsWith(str, expected))
return false;
str.remove_prefix(expected.size());
return true;
}
// Utility struct used by ConsumeDurationNumber() to parse decimal numbers.
// A ParsedDecimal represents the number `int_part` + `frac_part`/`frac_scale`,
// where:
// (i) 0 <= `frac_part` < `frac_scale` (implies `frac_part`/`frac_scale` < 1)
// (ii) `frac_scale` is 10^[number of digits after the decimal point]
//
// Example:
// -42 => {.int_part = -42, .frac_part = 0, .frac_scale = 1}
// 1.23 => {.int_part = 1, .frac_part = 23, .frac_scale = 100}
struct ParsedDecimal {
int64_t int_part = 0;
int64_t frac_part = 0;
int64_t frac_scale = 1;
};
// A helper for FromString() that tries to parse a leading number from the given
// StringPiece. |number_string| is modified to start from the first unconsumed
// char.
//
// Adapted from absl:
// https://cs.chromium.org/chromium/src/third_party/abseil-cpp/absl/time/duration.cc?l=807&rcl=2c22e9135f107a4319582ae52e2e3e6b201b6b7c
constexpr absl::optional<ParsedDecimal> ConsumeDurationNumber(
StringPiece& number_string) {
ParsedDecimal res;
StringPiece::const_iterator orig_start = number_string.begin();
// Parse contiguous digits.
for (; !number_string.empty(); number_string.remove_prefix(1)) {
const int d = number_string.front() - '0';
if (d < 0 || d >= 10)
break;
if (res.int_part > std::numeric_limits<int64_t>::max() / 10)
return absl::nullopt;
res.int_part *= 10;
if (res.int_part > std::numeric_limits<int64_t>::max() - d)
return absl::nullopt;
res.int_part += d;
}
const bool int_part_empty = number_string.begin() == orig_start;
if (number_string.empty() || number_string.front() != '.')
return int_part_empty ? absl::nullopt : absl::make_optional(res);
number_string.remove_prefix(1); // consume '.'
// Parse contiguous digits.
for (; !number_string.empty(); number_string.remove_prefix(1)) {
const int d = number_string.front() - '0';
if (d < 0 || d >= 10)
break;
DCHECK_LT(res.frac_part, res.frac_scale);
if (res.frac_scale <= std::numeric_limits<int64_t>::max() / 10) {
// |frac_part| will not overflow because it is always < |frac_scale|.
res.frac_part *= 10;
res.frac_part += d;
res.frac_scale *= 10;
}
}
return int_part_empty && res.frac_scale == 1 ? absl::nullopt
: absl::make_optional(res);
}
// A helper for FromString() that tries to parse a leading unit designator
// (e.g., ns, us, ms, s, m, h, d) from the given StringPiece. |unit_string| is
// modified to start from the first unconsumed char.
//
// Adapted from absl:
// https://cs.chromium.org/chromium/src/third_party/abseil-cpp/absl/time/duration.cc?l=841&rcl=2c22e9135f107a4319582ae52e2e3e6b201b6b7c
absl::optional<TimeDelta> ConsumeDurationUnit(StringPiece& unit_string) {
for (const auto& str_delta : {
std::make_pair("ns", Nanoseconds(1)),
std::make_pair("us", Microseconds(1)),
// Note: "ms" MUST be checked before "m" to ensure that milliseconds
// are not parsed as minutes.
std::make_pair("ms", Milliseconds(1)),
std::make_pair("s", Seconds(1)),
std::make_pair("m", Minutes(1)),
std::make_pair("h", Hours(1)),
std::make_pair("d", Days(1)),
}) {
if (ConsumePrefix(unit_string, str_delta.first))
return str_delta.second;
}
return absl::nullopt;
}
} // namespace
absl::optional<TimeDelta> TimeDeltaFromString(StringPiece duration_string) {
int sign = 1;
if (ConsumePrefix(duration_string, "-"))
sign = -1;
else
ConsumePrefix(duration_string, "+");
if (duration_string.empty())
return absl::nullopt;
// Handle special-case values that don't require units.
if (duration_string == "0")
return TimeDelta();
if (duration_string == "inf")
return sign == 1 ? TimeDelta::Max() : TimeDelta::Min();
TimeDelta delta;
while (!duration_string.empty()) {
absl::optional<ParsedDecimal> number_opt =
ConsumeDurationNumber(duration_string);
if (!number_opt.has_value())
return absl::nullopt;
absl::optional<TimeDelta> unit_opt = ConsumeDurationUnit(duration_string);
if (!unit_opt.has_value())
return absl::nullopt;
ParsedDecimal number = number_opt.value();
TimeDelta unit = unit_opt.value();
if (number.int_part != 0)
delta += sign * number.int_part * unit;
if (number.frac_part != 0)
delta +=
(static_cast<double>(sign) * number.frac_part / number.frac_scale) *
unit;
}
return delta;
}
} // namespace base
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