ckd_mul - cppreference.com

template< class type1, class type2, class type3 >
bool ckd_mul( type1* result, type2 a, type3 b );

Computes the multiplication x × y and stores the result into *result. The multiplication is performed as if both operands were represented in a signed integer type with infinite range, and the result was then converted from this integer type to type1. If the value assigned to *result correctly represents the mathematical result of the operation, it returns false. Otherwise, it returns true. In this case, the value assigned to *result is the mathematical result of the operation wrapped around to the width of *result.

Parameters

Return value

false if the value assigned to *result correctly represents the mathematical result of the multiplication, true otherwise.

Note

The function template ckd_mul has the same semantics as the corresponding type-generic macro with the same name specified in C23.

Each of the types type1, type2, and type3 is a cv-unqualified signed or unsigned integer type.

It is recommended to produce a diagnostic message if type2 or type3 are not suitable integer types, or if *result is not a modifiable lvalue of a suitable integer type.

Example

#include <climits>
#include <cstdint>
#include <print>
#include <stdckdint.h>

int main()
{
    uint8_t x;
    uint16_t y;
    uint16_t result_uint16;
    uint32_t result_uint32;
    bool overflow;

    x = 2;
    y = 21;
    overflow = ckd_mul(&result_uint16, x, y);
    std::println("{} * {} == {} ({})", x, y, result_uint16, overflow ? "Overflow" : "OK");

    x = 2;
    y = UINT16_MAX;
    overflow = ckd_mul(&result_uint16, x, y);
    std::println("{} * {} == {} ({})", x, y, result_uint16, overflow ? "Overflow" : "OK");

    x = 2;
    y = UINT16_MAX;
    overflow = ckd_mul(&result_uint32, x, y);
    std::println("{} * {} == {} ({})", x, y, result_uint32, overflow ? "Overflow" : "OK");
}

2 * 21 == 42 (OK)
2 * 65535 == 65534 (Overflow)
2 * 65535 == 131070 (OK)

References

See also