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[num-utils] add SafeMultiply() for overflow-safe multiplication (#12220)

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This commit introduces `SafeMultiply()` in `num_utils.hpp` as a
centralized and safe way to multiply two unsigned integers while
checking for overflow.

It updates `Coap::TxParameters::IsValid()` to use this new helper for
validating `TxParameters`, replacing a less robust local `Multiply`
implementation.

It also updates `Heap::CAlloc()` to use this function for safely
calculating the total allocation size.

Unit tests are updated to verify `SafeMultiply()` implementation.
This commit is contained in:
Abtin Keshavarzian
2025-12-17 13:01:36 -08:00
committed by GitHub
parent 79d973dce6
commit b9bbf71d34
5 changed files with 103 additions and 35 deletions
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tests/unit/test_serial_number.cpp
+35
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@@ -151,6 +151,41 @@ void TestNumUtils(void)
VerifyOrQuit(ThreeWayCompare<bool>(true, false) > 0);
VerifyOrQuit(ThreeWayCompare<bool>(false, true) < 0);
SuccessOrQuit(SafeMultiply<uint16_t>(0, 0, u16));
VerifyOrQuit(u16 == 0);
SuccessOrQuit(SafeMultiply<uint16_t>(0, 0xffff, u16));
VerifyOrQuit(u16 == 0);
SuccessOrQuit(SafeMultiply<uint16_t>(0xffff, 0, u16));
VerifyOrQuit(u16 == 0);
SuccessOrQuit(SafeMultiply<uint16_t>(1, 0xffff, u16));
VerifyOrQuit(u16 == 0xffff);
SuccessOrQuit(SafeMultiply<uint16_t>(0xffff, 1, u16));
VerifyOrQuit(u16 == 0xffff);
SuccessOrQuit(SafeMultiply<uint16_t>(256, 255, u16));
VerifyOrQuit(u16 == 65280);
SuccessOrQuit(SafeMultiply<uint16_t>(255, 256, u16));
VerifyOrQuit(u16 == 65280);
VerifyOrQuit(SafeMultiply<uint16_t>(256, 256, u16) == kErrorInvalidArgs);
for (uint16_t num = 2; num < 255; num++)
{
uint16_t div = 0xffff / num;
SuccessOrQuit(SafeMultiply<uint16_t>(num, div, u16));
VerifyOrQuit(u16 == num * div);
SuccessOrQuit(SafeMultiply<uint16_t>(div, num, u16));
VerifyOrQuit(u16 == num * div);
VerifyOrQuit(SafeMultiply<uint16_t>(num, div + 1, u16) == kErrorInvalidArgs);
VerifyOrQuit(SafeMultiply<uint16_t>(div + 1, num, u16) == kErrorInvalidArgs);
VerifyOrQuit(SafeMultiply<uint16_t>(num + 1, div, u16) == kErrorInvalidArgs);
VerifyOrQuit(SafeMultiply<uint16_t>(div, num + 1, u16) == kErrorInvalidArgs);
}
VerifyOrQuit(DivideAndRoundToClosest<uint8_t>(2, 1) == 2);
VerifyOrQuit(DivideAndRoundToClosest<uint8_t>(1, 3) == 0);
VerifyOrQuit(DivideAndRoundToClosest<uint8_t>(1, 2) == 1);