50 lines
1.0 KiB
Zig
50 lines
1.0 KiB
Zig
const builtin = @import("builtin");
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const compiler_rt = @import("../compiler_rt.zig");
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pub fn __muloti4(a: i128, b: i128, overflow: *c_int) callconv(.C) i128 {
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@setRuntimeSafety(builtin.is_test);
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const min = @bitCast(i128, @as(u128, 1 << (i128.bit_count - 1)));
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const max = ~min;
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overflow.* = 0;
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const r = a *% b;
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if (a == min) {
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if (b != 0 and b != 1) {
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overflow.* = 1;
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}
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return r;
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}
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if (b == min) {
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if (a != 0 and a != 1) {
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overflow.* = 1;
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}
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return r;
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}
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const sa = a >> (i128.bit_count - 1);
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const abs_a = (a ^ sa) -% sa;
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const sb = b >> (i128.bit_count - 1);
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const abs_b = (b ^ sb) -% sb;
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if (abs_a < 2 or abs_b < 2) {
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return r;
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}
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if (sa == sb) {
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if (abs_a > @divTrunc(max, abs_b)) {
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overflow.* = 1;
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}
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} else {
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if (abs_a > @divTrunc(min, -abs_b)) {
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overflow.* = 1;
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}
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}
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return r;
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}
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test "import muloti4" {
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_ = @import("muloti4_test.zig");
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}
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