The following built-in functions allow performing simple arithmetic operations together with checking whether the operations overflowed.
Built-in Functionbool__builtin_add_overflow(``type1``a,``type2``b,``type3``*res) .. index:: __builtin_sadd_overflow
Built-in Functionbool__builtin_sadd_overflow(inta,intb,int*res) .. index:: __builtin_saddl_overflow
Built-in Functionbool__builtin_saddl_overflow(longinta,longintb,longint*res) .. index:: __builtin_saddll_overflow
Built-in Functionbool__builtin_saddll_overflow(longlonginta,longlongintb,longint*res) .. index:: __builtin_uadd_overflow
Built-in Functionbool__builtin_uadd_overflow(unsignedinta,unsignedintb,unsignedint*res) .. index:: __builtin_uaddl_overflow
Built-in Functionbool__builtin_uaddl_overflow(unsignedlonginta,unsignedlongintb,unsignedlongint*res) .. index:: __builtin_uaddll_overflow
Built-in Functionbool__builtin_uaddll_overflow(unsignedlonglonginta,unsignedlonglongintb,unsignedlongint*res)These built-in functions promote the first two operands into infinite precision signed type and perform addition on those promoted operands. The result is then cast to the type the third pointer argument points to and stored there. If the stored result is equal to the infinite precision result, the built-in functions return false, otherwise they return true. As the addition is performed in infinite signed precision, these built-in functions have fully defined behavior for all argument values.
The first built-in function allows arbitrary integral types for operands and the result type must be pointer to some integer type, the rest of the built-in functions have explicit integer types.
The compiler will attempt to use hardware instructions to implement these built-in functions where possible, like conditional jump on overflow after addition, conditional jump on carry etc.
Built-in Functionbool__builtin_sub_overflow(``type1``a,``type2``b,``type3``*res) .. index:: __builtin_ssub_overflow
Built-in Functionbool__builtin_ssub_overflow(inta,intb,int*res) .. index:: __builtin_ssubl_overflow
Built-in Functionbool__builtin_ssubl_overflow(longinta,longintb,longint*res) .. index:: __builtin_ssubll_overflow
Built-in Functionbool__builtin_ssubll_overflow(longlonginta,longlongintb,longint*res) .. index:: __builtin_usub_overflow
Built-in Functionbool__builtin_usub_overflow(unsignedinta,unsignedintb,unsignedint*res) .. index:: __builtin_usubl_overflow
Built-in Functionbool__builtin_usubl_overflow(unsignedlonginta,unsignedlongintb,unsignedlongint*res) .. index:: __builtin_usubll_overflow
Built-in Functionbool__builtin_usubll_overflow(unsignedlonglonginta,unsignedlonglongintb,unsignedlongint*res)These built-in functions are similar to the add overflow checking built-in functions above, except they perform subtraction, subtract the second argument from the first one, instead of addition.
Built-in Functionbool__builtin_mul_overflow(``type1``a,``type2``b,``type3``*res) .. index:: __builtin_smul_overflow
Built-in Functionbool__builtin_smul_overflow(inta,intb,int*res) .. index:: __builtin_smull_overflow
Built-in Functionbool__builtin_smull_overflow(longinta,longintb,longint*res) .. index:: __builtin_smulll_overflow
Built-in Functionbool__builtin_smulll_overflow(longlonginta,longlongintb,longint*res) .. index:: __builtin_umul_overflow
Built-in Functionbool__builtin_umul_overflow(unsignedinta,unsignedintb,unsignedint*res) .. index:: __builtin_umull_overflow
Built-in Functionbool__builtin_umull_overflow(unsignedlonginta,unsignedlongintb,unsignedlongint*res) .. index:: __builtin_umulll_overflow
Built-in Functionbool__builtin_umulll_overflow(unsignedlonglonginta,unsignedlonglongintb,unsignedlongint*res)These built-in functions are similar to the add overflow checking built-in functions above, except they perform multiplication, instead of addition.