1const builtin = @import("builtin");
  2const std = @import("std");
  3const testing = std.testing;
  4const common = @import("common.zig");
  5const native_endian = builtin.cpu.arch.endian();
  6
  7pub const panic = common.panic;
  8
  9comptime {
 10    @export(&__mulsi3, .{ .name = "__mulsi3", .linkage = common.linkage, .visibility = common.visibility });
 11    if (common.want_aeabi) {
 12        @export(&__aeabi_lmul, .{ .name = "__aeabi_lmul", .linkage = common.linkage, .visibility = common.visibility });
 13    } else {
 14        @export(&__muldi3, .{ .name = "__muldi3", .linkage = common.linkage, .visibility = common.visibility });
 15    }
 16    if (common.want_windows_v2u64_abi) {
 17        @export(&__multi3_windows_x86_64, .{ .name = "__multi3", .linkage = common.linkage, .visibility = common.visibility });
 18    } else {
 19        @export(&__multi3, .{ .name = "__multi3", .linkage = common.linkage, .visibility = common.visibility });
 20    }
 21}
 22
 23pub fn __mulsi3(a: i32, b: i32) callconv(.c) i32 {
 24    var ua: u32 = @bitCast(a);
 25    var ub: u32 = @bitCast(b);
 26    var r: u32 = 0;
 27
 28    while (ua > 0) {
 29        if ((ua & 1) != 0) r +%= ub;
 30        ua >>= 1;
 31        ub <<= 1;
 32    }
 33
 34    return @bitCast(r);
 35}
 36
 37pub fn __muldi3(a: i64, b: i64) callconv(.c) i64 {
 38    return mulX(i64, a, b);
 39}
 40
 41fn __aeabi_lmul(a: i64, b: i64) callconv(.{ .arm_aapcs = .{} }) i64 {
 42    return mulX(i64, a, b);
 43}
 44
 45inline fn mulX(comptime T: type, a: T, b: T) T {
 46    const word_t = common.HalveInt(T, false);
 47    const x = word_t{ .all = a };
 48    const y = word_t{ .all = b };
 49    var r = switch (T) {
 50        i64, i128 => word_t{ .all = muldXi(word_t.HalfT, x.s.low, y.s.low) },
 51        else => unreachable,
 52    };
 53    r.s.high +%= x.s.high *% y.s.low +% x.s.low *% y.s.high;
 54    return r.all;
 55}
 56
 57fn DoubleInt(comptime T: type) type {
 58    return switch (T) {
 59        u32 => i64,
 60        u64 => i128,
 61        i32 => i64,
 62        i64 => i128,
 63        else => unreachable,
 64    };
 65}
 66
 67fn muldXi(comptime T: type, a: T, b: T) DoubleInt(T) {
 68    const DT = DoubleInt(T);
 69    const word_t = common.HalveInt(DT, false);
 70    const bits_in_word_2 = @sizeOf(T) * 8 / 2;
 71    const lower_mask = (~@as(T, 0)) >> bits_in_word_2;
 72
 73    var r: word_t = undefined;
 74    r.s.low = (a & lower_mask) *% (b & lower_mask);
 75    var t: T = r.s.low >> bits_in_word_2;
 76    r.s.low &= lower_mask;
 77    t += (a >> bits_in_word_2) *% (b & lower_mask);
 78    r.s.low +%= (t & lower_mask) << bits_in_word_2;
 79    r.s.high = t >> bits_in_word_2;
 80    t = r.s.low >> bits_in_word_2;
 81    r.s.low &= lower_mask;
 82    t +%= (b >> bits_in_word_2) *% (a & lower_mask);
 83    r.s.low +%= (t & lower_mask) << bits_in_word_2;
 84    r.s.high +%= t >> bits_in_word_2;
 85    r.s.high +%= (a >> bits_in_word_2) *% (b >> bits_in_word_2);
 86    return r.all;
 87}
 88
 89pub fn __multi3(a: i128, b: i128) callconv(.c) i128 {
 90    return mulX(i128, a, b);
 91}
 92
 93const v2u64 = @Vector(2, u64);
 94
 95fn __multi3_windows_x86_64(a: v2u64, b: v2u64) callconv(.c) v2u64 {
 96    return @bitCast(mulX(i128, @as(i128, @bitCast(a)), @as(i128, @bitCast(b))));
 97}
 98
 99test {
100    _ = @import("mulXi3_test.zig");
101}