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AK: Fix some overflows/underflows that weren't properly handled

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Based on #5699. Closes #5699.
This commit is contained in:
Ben Wiederhake 2021-03-11 22:12:04 +01:00 • committed by Andreas Kling
parent 8a8bdb2cd7
commit 81079ae616
3 changed files with 127 additions and 94 deletions
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45
AK/Time.h
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@ -26,6 +26,7 @@
#pragma once
#include <AK/Assertions.h>
#include <AK/Platform.h>
#include <AK/Types.h>
@ -100,18 +101,51 @@ public:
return *this;
}
private:
// This must be part of the header in order to make the various 'from_*' functions constexpr.
// However, sane_mod can only deal with a limited range of values for 'denominator', so this can't be made public.
ALWAYS_INLINE static constexpr i64 sane_mod(i64& numerator, i64 denominator)
{
VERIFY(2 <= denominator && denominator <= 1'000'000'000);
// '%' in C/C++ does not work in the obvious way:
// For example, -9 % 7 is -2, not +5.
// However, we want a representation like "(-2)*7 + (+5)".
i64 dividend = numerator / denominator;
numerator %= denominator;
if (numerator < 0) {
// Does not overflow: different signs.
numerator += denominator;
// Does not underflow: denominator >= 2.
dividend -= 1;
}
return dividend;
}
ALWAYS_INLINE static constexpr i32 sane_mod(i32& numerator, i32 denominator)
{
i64 numerator_64 = numerator;
i64 dividend = sane_mod(numerator_64, denominator);
// Does not underflow: numerator can only become smaller.
numerator = numerator_64;
// Does not overflow: Will be smaller than original value of 'numerator'.
return dividend;
}
public:
constexpr static Time from_seconds(i64 seconds) { return Time(seconds, 0); }
constexpr static Time from_nanoseconds(i64 nanoseconds)
{
return Time(nanoseconds / 1'000'000'000, nanoseconds % 1'000'000'000);
i64 seconds = sane_mod(nanoseconds, 1'000'000'000);
return Time(seconds, nanoseconds);
}
constexpr static Time from_microseconds(i64 microseconds)
{
return Time(microseconds / 1'000'000, (microseconds % 1'000'000) * 1'000);
i64 seconds = sane_mod(microseconds, 1'000'000);
return Time(seconds, microseconds * 1'000);
}
constexpr static Time from_milliseconds(i64 milliseconds)
{
return Time(milliseconds / 1'000, (milliseconds % 1'000) * 1'000'000);
i64 seconds = sane_mod(milliseconds, 1'000);
return Time(seconds, milliseconds * 1'000'000);
}
static Time from_timespec(const struct timespec&);
static Time from_timeval(const struct timeval&);
@ -119,16 +153,17 @@ public:
static Time zero() { return Time(0, 0); };
static Time max() { return Time(0x7fff'ffff'ffff'ffffLL, 999'999'999); };
// Truncates "2.8 seconds" to 2 seconds.
// Truncates "-2.8 seconds" to -2 seconds.
// Truncates towards zero (2.8s to 2s, -2.8s to -2s).
i64 to_truncated_seconds() const;
i64 to_truncated_milliseconds() const;
i64 to_truncated_microseconds() const;
// Rounds away from zero (2.3s to 3s, -2.3s to -3s).
i64 to_seconds() const;
i64 to_milliseconds() const;
i64 to_microseconds() const;
i64 to_nanoseconds() const;
timespec to_timespec() const;
// Rounds towards -inf (it was the easiest to implement).
timeval to_timeval() const;
bool is_zero() const { return !m_seconds && !m_nanoseconds; }