safemath

Header-only overflow-safe size math for C and C++.

safemath.h provides checked helpers for addition, subtraction, multiplication, allocation sizing, offset bounds, and power-of-two alignment.

Contract

• Public API is bool-returning.
• out == NULL returns false for every result-writing API.
• On failure, *out is unchanged when out != NULL.
• Zero-sized element calculations are mathematically valid.
• sm_offset_add() uses exclusive-end semantics.
• result == limit is valid and represents one-past-end.
• The return value does not identify the exact failure cause.
• Return values must be checked.
• The library has no third-party runtime dependencies. Standard headers are still required.

API

• sm_add, sm_sub, sm_mul
• sm_array_bytes, sm_alloc_bytes, sm_offset_add
• sm_is_pow2, sm_align_up, sm_align_up_bytes

Version macros:

• SAFEMATH_VERSION_MAJOR
• SAFEMATH_VERSION_MINOR
• SAFEMATH_VERSION_PATCH
• SAFEMATH_VERSION_NUMBER
• SAFEMATH_VERSION_STRING

Optional diagnostics:

• SAFEMATH_NODISCARD
• SAFEMATH_NO_NODISCARD

Builtin selection:

• SAFEMATH_FORCE_PORTABLE
• SAFEMATH_FORCE_BUILTINS

Defining both force macros is a compile-time error.

Use

#include "safemath.h"

size_t bytes;
if (!sm_array_bytes(&bytes, count, sizeof(struct record))) {
    return false;
}

CMake package

Install and consume the header through the exported interface target:

find_package(safemath CONFIG REQUIRED)
target_link_libraries(app PRIVATE safemath::safemath)

Verified locally

Item	Result
Windows x64, Visual Studio 2022 Community, MSVC 19.42.34444.0	passed
C99 build (clang -std=c99 under vcvars64)	passed
C++11 build (clang++ -std=c++11 under vcvars64)	passed
C test build (cl /std:c11)	passed
C++ wrapper build (cl /std:c++14)	passed
CTest suite with auto and forced-portable paths	passed
Package install and consumer smoke through find_package	passed
Forced-builtin compile on this MSVC toolchain	failed as intended with a clear #error
WSL Ubuntu-24.04 verification	complete, user-reported

Sources of truth

• API contracts
• Portability notes
• Cookbook
• Verification log