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muloXi4_genericFast

mulo.muloXi4_genericFast

inline fn muloXi4_genericFast(comptime ST: type, a: ST, b: ST, overflow: *c_int) ST

File

lib/compiler_rt/mulo.zig:38

Code

inline fn muloXi4_genericFast(comptime ST: type, a: ST, b: ST, overflow: *c_int) ST {
    overflow.* = 0;
    const EST = switch (ST) {
        i32 => i64,
        i64 => i128,
        i128 => i256,
        else => unreachable,
    };
    const min = math.minInt(ST);
    const max = math.maxInt(ST);
    const res: EST = @as(EST, a) * @as(EST, b);
    //invariant: -2^{bitwidth(EST)} < res < 2^{bitwidth(EST)-1}
    if (res < min or max < res)
        overflow.* = 1;
    return @as(ST, @truncate(res));
}