55 lines
1.5 KiB
Zig
55 lines
1.5 KiB
Zig
const builtin = @import("builtin");
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// Ported from
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// https://github.com/llvm/llvm-project/blob/llvmorg-9.0.0/compiler-rt/lib/builtins/muldi3.c
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const dwords = extern union {
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all: i64,
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s: switch (builtin.endian) {
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.Little => extern struct {
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low: u32,
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high: u32,
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},
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.Big => extern struct {
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high: u32,
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low: u32,
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},
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},
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};
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fn __muldsi3(a: u32, b: u32) i64 {
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@setRuntimeSafety(builtin.is_test);
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const bits_in_word_2 = @sizeOf(i32) * 8 / 2;
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const lower_mask = (~u32(0)) >> bits_in_word_2;
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var r: dwords = undefined;
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r.s.low = (a & lower_mask) *% (b & lower_mask);
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var t: u32 = r.s.low >> bits_in_word_2;
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r.s.low &= lower_mask;
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t += (a >> bits_in_word_2) *% (b & lower_mask);
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r.s.low +%= (t & lower_mask) << bits_in_word_2;
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r.s.high = t >> bits_in_word_2;
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t = r.s.low >> bits_in_word_2;
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r.s.low &= lower_mask;
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t +%= (b >> bits_in_word_2) *% (a & lower_mask);
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r.s.low +%= (t & lower_mask) << bits_in_word_2;
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r.s.high +%= t >> bits_in_word_2;
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r.s.high +%= (a >> bits_in_word_2) *% (b >> bits_in_word_2);
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return r.all;
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}
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pub extern fn __muldi3(a: i64, b: i64) i64 {
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@setRuntimeSafety(builtin.is_test);
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const x = dwords{ .all = a };
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const y = dwords{ .all = b };
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var r = dwords{ .all = __muldsi3(x.s.low, y.s.low) };
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r.s.high +%= x.s.high *% y.s.low +% x.s.low *% y.s.high;
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return r.all;
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}
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test "import muldi3" {
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_ = @import("muldi3_test.zig");
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}
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