50 lines
1.4 KiB
Zig
50 lines
1.4 KiB
Zig
// SPDX-License-Identifier: MIT
|
|
// Copyright (c) 2015-2020 Zig Contributors
|
|
// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
|
|
// The MIT license requires this copyright notice to be included in all copies
|
|
// and substantial portions of the software.
|
|
const builtin = @import("builtin");
|
|
const compiler_rt = @import("../compiler_rt.zig");
|
|
const maxInt = std.math.maxInt;
|
|
const minInt = std.math.minInt;
|
|
|
|
pub fn __mulodi4(a: i64, b: i64, overflow: *c_int) callconv(.C) i64 {
|
|
@setRuntimeSafety(builtin.is_test);
|
|
|
|
const min = @bitCast(i64, @as(u64, 1 << (64 - 1)));
|
|
const max = ~min;
|
|
|
|
overflow.* = 0;
|
|
const result = a *% b;
|
|
|
|
// Edge cases
|
|
if (a == min) {
|
|
if (b != 0 and b != 1) overflow.* = 1;
|
|
return result;
|
|
}
|
|
if (b == min) {
|
|
if (a != 0 and a != 1) overflow.* = 1;
|
|
return result;
|
|
}
|
|
|
|
// Take absolute value of a and b via abs(x) = (x^(x >> 63)) - (x >> 63).
|
|
const abs_a = (a ^ (a >> 63)) -% (a >> 63);
|
|
const abs_b = (b ^ (b >> 63)) -% (b >> 63);
|
|
|
|
// Unitary magnitude, cannot have overflow
|
|
if (abs_a < 2 or abs_b < 2) return result;
|
|
|
|
// Compare the signs of the operands
|
|
if ((a ^ b) >> 63 != 0) {
|
|
if (abs_a > @divTrunc(max, abs_b)) overflow.* = 1;
|
|
} else {
|
|
if (abs_a > @divTrunc(min, -abs_b)) overflow.* = 1;
|
|
}
|
|
|
|
return result;
|
|
}
|
|
|
|
test "import mulodi4" {
|
|
_ = @import("mulodi4_test.zig");
|
|
}
|