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Something like this? https://godbolt.org/z/6nod5e. It even produces almost identical assembly.

The equivalent to checked_mul is __builtin_mul_overflow, which is a compiler builtin: https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.... Similarly, saturating_sub seems like it can be implemented with __builtin_sub_overflow.

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Would those work on any compiler, or are they compiler-specific? If those are non-standard compiler-specific extensions, not even a library, is it truly a part of C++?

While I'll grant that Rust only has one fully functional compiler at this time, those functions have been part of Rust's corelib since 1.0. Any Rust compiler would have to support them.

They're not part of the standard, but gcc, clang, and icc (Intel) support them. Alternatively, you could emit the correct instructions in an asm block on supported architectures (x86: 'jo'/'jno' for jumps, 'cmovo'/'cmovno' for conditional moves [1]) or reimplement the operations in software [2]

[1] https://www.felixcloutier.com/x86/jcc and https://www.felixcloutier.com/x86/cmovcc

[2] https://wiki.sei.cmu.edu/confluence/display/c/INT32-C.+Ensur....

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