optimized memcpy #18912
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,149 +1,213 @@ | ||
| const std = @import("std"); | ||
| const assert = std.debug.assert; | ||
| const common = @import("./common.zig"); | ||
| const builtin = @import("builtin"); | ||
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| comptime { | ||
| if (builtin.object_format != .c) { | ||
| const export_options: std.builtin.ExportOptions = .{ | ||
| .name = "memcpy", | ||
| .linkage = common.linkage, | ||
| .visibility = common.visibility, | ||
| }; | ||
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| if (builtin.mode == .ReleaseSmall) | ||
| @export(&memcpySmall, export_options) | ||
| else | ||
| @export(&memcpyFast, export_options); | ||
| } | ||
| } | ||
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| const Element = if (std.simd.suggestVectorLength(u8)) |vec_size| | ||
| @Type(.{ .vector = .{ | ||
| .child = u8, | ||
| .len = vec_size, | ||
| } }) | ||
| else | ||
| usize; | ||
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| comptime { | ||
| assert(@sizeOf(Element) >= @alignOf(Element)); | ||
| assert(std.math.isPowerOfTwo(@sizeOf(Element))); | ||
|
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There was a problem hiding this comment. All types have a size that is a multiple of its alignment, therefore the first condition isn't checking for anything. If you need a power of two, just use |
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| } | ||
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| fn memcpySmall(noalias dest: ?[*]u8, noalias src: ?[*]const u8, len: usize) callconv(.C) ?[*]u8 { | ||
| @setRuntimeSafety(builtin.is_test); | ||
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| for (0..len) |i| { | ||
| dest.?[i] = src.?[i]; | ||
| } | ||
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| return dest; | ||
| } | ||
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| fn memcpyFast(noalias dest: ?[*]u8, noalias src: ?[*]const u8, len: usize) callconv(.C) ?[*]u8 { | ||
| @setRuntimeSafety(builtin.is_test); | ||
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| const small_limit = 2 * @sizeOf(Element); | ||
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| if (copySmallLength(small_limit, dest.?, src.?, len)) return dest; | ||
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| copyForwards(dest.?, src.?, len); | ||
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| return dest; | ||
| } | ||
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| inline fn copySmallLength( | ||
| comptime small_limit: comptime_int, | ||
| dest: [*]u8, | ||
| src: [*]const u8, | ||
| len: usize, | ||
| ) bool { | ||
| if (len < 16) { | ||
| copyLessThan16(dest, src, len); | ||
| return true; | ||
| } | ||
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| if (comptime 2 < (std.math.log2(small_limit) + 1) / 2) { | ||
| if (copy16ToSmallLimit(small_limit, dest, src, len)) return true; | ||
| } | ||
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| return false; | ||
| } | ||
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| inline fn copyLessThan16( | ||
| dest: [*]u8, | ||
| src: [*]const u8, | ||
| len: usize, | ||
| ) void { | ||
| @setRuntimeSafety(builtin.is_test); | ||
| if (len < 4) { | ||
| if (len == 0) return; | ||
| dest[0] = src[0]; | ||
| dest[len / 2] = src[len / 2]; | ||
| dest[len - 1] = src[len - 1]; | ||
| return; | ||
| } | ||
| copyRange4(4, dest, src, len); | ||
| } | ||
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| inline fn copy16ToSmallLimit( | ||
| comptime small_limit: comptime_int, | ||
| dest: [*]u8, | ||
| src: [*]const u8, | ||
| len: usize, | ||
| ) bool { | ||
| @setRuntimeSafety(builtin.is_test); | ||
| inline for (2..(std.math.log2(small_limit) + 1) / 2 + 1) |p| { | ||
| const limit = 1 << (2 * p); | ||
| if (len < limit) { | ||
| copyRange4(limit / 4, dest, src, len); | ||
| return true; | ||
| } | ||
| } | ||
| return false; | ||
| } | ||
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| inline fn copyForwards( | ||
| noalias dest: [*]u8, | ||
| noalias src: [*]const u8, | ||
| len: usize, | ||
| ) void { | ||
| @setRuntimeSafety(builtin.is_test); | ||
| assert(len >= 2 * @sizeOf(Element)); | ||
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| dest[0..@sizeOf(Element)].* = src[0..@sizeOf(Element)].*; | ||
| const alignment_offset = @alignOf(Element) - @intFromPtr(src) % @alignOf(Element); | ||
| const n = len - alignment_offset; | ||
| const d = dest + alignment_offset; | ||
| const s = src + alignment_offset; | ||
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| copyBlocksAlignedSource(@ptrCast(d), @alignCast(@ptrCast(s)), n); | ||
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| // copy last `@sizeOf(Element)` bytes unconditionally, since block copy | ||
| // methods only copy a multiple of `@sizeOf(Element)` bytes. | ||
| const offset = len - @sizeOf(Element); | ||
| dest[offset..][0..@sizeOf(Element)].* = src[offset..][0..@sizeOf(Element)].*; | ||
| } | ||
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| inline fn copyBlocksAlignedSource( | ||
| noalias dest: [*]align(1) Element, | ||
| noalias src: [*]const Element, | ||
| max_bytes: usize, | ||
| ) void { | ||
| copyBlocks(dest, src, max_bytes); | ||
| } | ||
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| /// Copies the largest multiple of `@sizeOf(T)` bytes from `src` to `dest`, | ||
| /// that is less than `max_bytes` where `T` is the child type of `src` and | ||
| /// `dest`. | ||
| inline fn copyBlocks( | ||
| noalias dest: anytype, | ||
| noalias src: anytype, | ||
| max_bytes: usize, | ||
| ) void { | ||
| @setRuntimeSafety(builtin.is_test); | ||
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| const T = @typeInfo(@TypeOf(dest)).pointer.child; | ||
| comptime assert(T == @typeInfo(@TypeOf(src)).pointer.child); | ||
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| const loop_count = max_bytes / @sizeOf(T); | ||
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| for (dest[0..loop_count], src[0..loop_count]) |*d, s| { | ||
| d.* = s; | ||
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| } | ||
| } | ||
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| /// copy `len` bytes from `src` to `dest`; `len` must be in the range | ||
| /// `[copy_len, 4 * copy_len)`. | ||
| inline fn copyRange4( | ||
| comptime copy_len: comptime_int, | ||
| noalias dest: [*]u8, | ||
| noalias src: [*]const u8, | ||
| len: usize, | ||
| ) void { | ||
| @setRuntimeSafety(builtin.is_test); | ||
| comptime assert(std.math.isPowerOfTwo(copy_len)); | ||
| assert(len >= copy_len); | ||
| assert(len < 4 * copy_len); | ||
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| const a = len & (copy_len * 2); | ||
| const b = a / 2; | ||
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| const last = len - copy_len; | ||
| const pen = last - b; | ||
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| dest[0..copy_len].* = src[0..copy_len].*; | ||
| dest[b..][0..copy_len].* = src[b..][0..copy_len].*; | ||
| dest[pen..][0..copy_len].* = src[pen..][0..copy_len].*; | ||
| dest[last..][0..copy_len].* = src[last..][0..copy_len].*; | ||
| } | ||
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| test { | ||
| const S = struct { | ||
| fn testFunc(comptime copy_func: anytype) !void { | ||
| const max_len = 1024; | ||
| var buffer: [max_len + @alignOf(Element) - 1]u8 align(@alignOf(Element)) = undefined; | ||
| for (&buffer, 0..) |*b, i| { | ||
| b.* = @intCast(i % 97); | ||
| } | ||
| var dest: [max_len + @alignOf(Element) - 1]u8 align(@alignOf(Element)) = undefined; | ||
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| for (0..max_len) |copy_len| { | ||
| for (0..@alignOf(Element)) |s_offset| { | ||
| for (0..@alignOf(Element)) |d_offset| { | ||
| @memset(&dest, 0xff); | ||
| const s = buffer[s_offset..][0..copy_len]; | ||
| const d = dest[d_offset..][0..copy_len]; | ||
| _ = copy_func(@ptrCast(d.ptr), @ptrCast(s.ptr), s.len); | ||
| std.testing.expectEqualSlices(u8, s, d) catch |e| { | ||
| std.debug.print("error encountered for length={d}, s_offset={d}, d_offset={d}\n", .{ | ||
| copy_len, s_offset, d_offset, | ||
| }); | ||
| return e; | ||
| }; | ||
| } | ||
| } | ||
| } | ||
| } | ||
| }; | ||
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| try S.testFunc(memcpySmall); | ||
| try S.testFunc(memcpyFast); | ||
| } | ||
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