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Fix MulDivSaturate to avoid overflow

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Thanks to Caolan
https://gerrit.libreoffice.org/c/core/+/110839/comments/5c47cab2_b0523546

> oss-fuzz has come up with a case of n 9223372036854775807 m 72 d 127
>
> include/o3tl/unit_conversion.hxx:105:28: runtime error: signed integer
> overflow: 9223372036854775807 + 63 cannot be represented in type 'long'

Change-Id: I0fe26f6c854a90cf577a60528d15f3da5471b914
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/141711
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
This commit is contained in:
Mike Kaganski 2022-10-24 09:37:37 +02:00
parent 87aef8ff9f
commit 635a0b426e
3 changed files with 17 additions and 6 deletions
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4
include/o3tl/safeint.hxx
View file

@ -27,7 +27,7 @@
namespace o3tl
{
template <typename T> inline T saturating_add(T a, T b)
template <typename T> inline constexpr T saturating_add(T a, T b)
{
if (b >= 0) {
if (a <= std::numeric_limits<T>::max() - b) {
@ -44,7 +44,7 @@ template <typename T> inline T saturating_add(T a, T b)
}
}
template <typename T> inline T saturating_sub(T a, T b)
template <typename T> inline constexpr T saturating_sub(T a, T b)
{
if (b >= 0) {
if (a >= std::numeric_limits<T>::min() + b) {

17
include/o3tl/unit_conversion.hxx
View file

@ -98,11 +98,20 @@ constexpr sal_Int64 MulDiv(I n, sal_Int64 m, sal_Int64 d, bool& bOverflow, sal_I
template <typename I, std::enable_if_t<std::is_integral_v<I>, int> = 0>
constexpr sal_Int64 MulDivSaturate(I n, sal_Int64 m, sal_Int64 d)
{
if (!isBetween(n, (SAL_MIN_INT64 + d / 2) / m, (SAL_MAX_INT64 - d / 2) / m))
if (sal_Int64 d_2 = d / 2; !isBetween(n, (SAL_MIN_INT64 + d_2) / m, (SAL_MAX_INT64 - d_2) / m))
{
if (m > d && !isBetween(n, SAL_MIN_INT64 / m * d + d / 2, SAL_MAX_INT64 / m * d - d / 2))
return n > 0 ? SAL_MAX_INT64 : SAL_MIN_INT64; // saturate
return (n >= 0 ? n + d / 2 : n - d / 2) / d * m; // divide before multiplication
if (n >= 0)
{
if (m > d && std::make_unsigned_t<I>(n) > sal_uInt64(SAL_MAX_INT64 / m * d - d_2))
return SAL_MAX_INT64; // saturate
return saturating_add<sal_uInt64>(n, d_2) / d * m; // divide before multiplication
}
else if constexpr (std::is_signed_v<I>) // n < 0; don't compile for unsigned n
{
if (m > d && n < SAL_MIN_INT64 / m * d + d_2)
return SAL_MIN_INT64; // saturate
return saturating_sub<sal_Int64>(n, d_2) / d * m; // divide before multiplication
}
}
return MulDiv(n, m, d);
}

2
o3tl/qa/test-unit_conversion.cxx
View file

@ -878,4 +878,6 @@ static_assert(o3tl::toTwips(20, o3tl::Length::mm) == 1134);
// 847 100thmm used to represent 24pt
static_assert(o3tl::convert(24, o3tl::Length::pt, o3tl::Length::mm100) == 847);
static_assert(o3tl::convertSaturate(SAL_MAX_INT64, 72, 127) == 5228998320106644552); // no overflow
/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */