131 lines
4.0 KiB
Zig
131 lines
4.0 KiB
Zig
const std = @import("std");
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const builtin = std.builtin;
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const Log2Int = std.math.Log2Int;
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fn Dwords(comptime T: type, comptime signed_half: bool) type {
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return extern union {
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pub const HalfTU = std.meta.IntType(false, @divExact(T.bit_count, 2));
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pub const HalfTS = std.meta.IntType(true, @divExact(T.bit_count, 2));
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pub const HalfT = if (signed_half) HalfTS else HalfTU;
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all: T,
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s: if (builtin.endian == .Little)
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struct { low: HalfT, high: HalfT }
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else
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struct { high: HalfT, low: HalfT },
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};
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}
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// Arithmetic shift left
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// Precondition: 0 <= b < bits_in_dword
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pub fn ashlXi3(comptime T: type, a: T, b: i32) T {
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const dwords = Dwords(T, false);
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const S = Log2Int(dwords.HalfT);
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const input = dwords{ .all = a };
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var output: dwords = undefined;
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if (b >= dwords.HalfT.bit_count) {
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output.s.low = 0;
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output.s.high = input.s.low << @intCast(S, b - dwords.HalfT.bit_count);
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} else if (b == 0) {
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return a;
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} else {
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output.s.low = input.s.low << @intCast(S, b);
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output.s.high = input.s.high << @intCast(S, b);
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output.s.high |= input.s.low >> @intCast(S, dwords.HalfT.bit_count - b);
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}
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return output.all;
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}
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// Arithmetic shift right
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// Precondition: 0 <= b < T.bit_count
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pub fn ashrXi3(comptime T: type, a: T, b: i32) T {
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const dwords = Dwords(T, true);
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const S = Log2Int(dwords.HalfT);
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const input = dwords{ .all = a };
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var output: dwords = undefined;
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if (b >= dwords.HalfT.bit_count) {
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output.s.high = input.s.high >> (dwords.HalfT.bit_count - 1);
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output.s.low = input.s.high >> @intCast(S, b - dwords.HalfT.bit_count);
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} else if (b == 0) {
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return a;
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} else {
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output.s.high = input.s.high >> @intCast(S, b);
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output.s.low = input.s.high << @intCast(S, dwords.HalfT.bit_count - b);
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// Avoid sign-extension here
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output.s.low |= @bitCast(
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dwords.HalfT,
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@bitCast(dwords.HalfTU, input.s.low) >> @intCast(S, b),
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);
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}
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return output.all;
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}
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// Logical shift right
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// Precondition: 0 <= b < T.bit_count
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pub fn lshrXi3(comptime T: type, a: T, b: i32) T {
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const dwords = Dwords(T, false);
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const S = Log2Int(dwords.HalfT);
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const input = dwords{ .all = a };
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var output: dwords = undefined;
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if (b >= dwords.HalfT.bit_count) {
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output.s.high = 0;
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output.s.low = input.s.high >> @intCast(S, b - dwords.HalfT.bit_count);
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} else if (b == 0) {
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return a;
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} else {
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output.s.high = input.s.high >> @intCast(S, b);
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output.s.low = input.s.high << @intCast(S, dwords.HalfT.bit_count - b);
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output.s.low |= input.s.low >> @intCast(S, b);
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}
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return output.all;
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}
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pub fn __ashldi3(a: i64, b: i32) callconv(.C) i64 {
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return @call(.{ .modifier = .always_inline }, ashlXi3, .{ i64, a, b });
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}
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pub fn __ashlti3(a: i128, b: i32) callconv(.C) i128 {
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return @call(.{ .modifier = .always_inline }, ashlXi3, .{ i128, a, b });
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}
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pub fn __ashrdi3(a: i64, b: i32) callconv(.C) i64 {
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return @call(.{ .modifier = .always_inline }, ashrXi3, .{ i64, a, b });
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}
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pub fn __ashrti3(a: i128, b: i32) callconv(.C) i128 {
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return @call(.{ .modifier = .always_inline }, ashrXi3, .{ i128, a, b });
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}
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pub fn __lshrdi3(a: i64, b: i32) callconv(.C) i64 {
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return @call(.{ .modifier = .always_inline }, lshrXi3, .{ i64, a, b });
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}
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pub fn __lshrti3(a: i128, b: i32) callconv(.C) i128 {
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return @call(.{ .modifier = .always_inline }, lshrXi3, .{ i128, a, b });
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}
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pub fn __aeabi_llsl(a: i64, b: i32) callconv(.AAPCS) i64 {
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return __ashldi3(a, b);
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}
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pub fn __aeabi_lasr(a: i64, b: i32) callconv(.AAPCS) i64 {
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return __ashrdi3(a, b);
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}
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pub fn __aeabi_llsr(a: i64, b: i32) callconv(.AAPCS) i64 {
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return __lshrdi3(a, b);
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}
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test "" {
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_ = @import("ashrdi3_test.zig");
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_ = @import("ashrti3_test.zig");
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_ = @import("ashldi3_test.zig");
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_ = @import("ashlti3_test.zig");
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_ = @import("lshrdi3_test.zig");
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_ = @import("lshrti3_test.zig");
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}
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