76 lines
2.1 KiB
Zig
76 lines
2.1 KiB
Zig
//! Ported from git@github.com:llvm-project/llvm-project-20170507.git
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//! ae684fad6d34858c014c94da69c15e7774a633c3
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//! 2018-08-13
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const std = @import("std");
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const builtin = @import("builtin");
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const native_endian = builtin.cpu.arch.endian();
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const common = @import("common.zig");
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pub const panic = common.panic;
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comptime {
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if (common.want_windows_v2u64_abi) {
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@export(__multi3_windows_x86_64, .{ .name = "__multi3", .linkage = common.linkage });
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} else {
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@export(__multi3, .{ .name = "__multi3", .linkage = common.linkage });
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}
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}
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pub fn __multi3(a: i128, b: i128) callconv(.C) i128 {
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return mul(a, b);
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}
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const v2u64 = @Vector(2, u64);
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fn __multi3_windows_x86_64(a: v2u64, b: v2u64) callconv(.C) v2u64 {
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return @bitCast(v2u64, mul(@bitCast(i128, a), @bitCast(i128, b)));
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}
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inline fn mul(a: i128, b: i128) i128 {
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const x = twords{ .all = a };
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const y = twords{ .all = b };
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var r = twords{ .all = mulddi3(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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fn mulddi3(a: u64, b: u64) i128 {
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const bits_in_dword_2 = (@sizeOf(i64) * 8) / 2;
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const lower_mask = ~@as(u64, 0) >> bits_in_dword_2;
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var r: twords = undefined;
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r.s.low = (a & lower_mask) *% (b & lower_mask);
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var t: u64 = r.s.low >> bits_in_dword_2;
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r.s.low &= lower_mask;
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t +%= (a >> bits_in_dword_2) *% (b & lower_mask);
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r.s.low +%= (t & lower_mask) << bits_in_dword_2;
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r.s.high = t >> bits_in_dword_2;
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t = r.s.low >> bits_in_dword_2;
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r.s.low &= lower_mask;
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t +%= (b >> bits_in_dword_2) *% (a & lower_mask);
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r.s.low +%= (t & lower_mask) << bits_in_dword_2;
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r.s.high +%= t >> bits_in_dword_2;
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r.s.high +%= (a >> bits_in_dword_2) *% (b >> bits_in_dword_2);
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return r.all;
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}
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const twords = extern union {
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all: i128,
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s: S,
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const S = if (native_endian == .Little)
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extern struct {
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low: u64,
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high: u64,
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}
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else
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extern struct {
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high: u64,
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low: u64,
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};
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};
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test {
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_ = @import("multi3_test.zig");
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}
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