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std.hash.crc: simplify api
This removes the two original implementations in favour of the single generic one based on the Algorithm type. Previously we had three, very similar implementations which was somewhat confusing when knowing what one should actually be used. The previous polynomials all have equivalent variants available when using the Algorithm type.
This commit is contained in:
Marc Tiehuis
parent
c231d94960
commit
ef5618fcd5
@ -7,8 +7,7 @@ pub const Polynomial = impl.Polynomial;
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pub const Crc32WithPoly = impl.Crc32WithPoly;
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pub const Crc32SmallWithPoly = impl.Crc32SmallWithPoly;
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// IEEE is by far the most common CRC and so is aliased by default.
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pub const Crc32 = Crc32WithPoly(.IEEE);
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pub const Crc32 = Crc32IsoHdlc;
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test {
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_ = @import("crc/test.zig");
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@ -822,6 +821,14 @@ pub const Crc32Jamcrc = Crc(u32, .{
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.xor_output = 0x00000000,
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});
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pub const Crc32Koopman = Crc(u32, .{
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.polynomial = 0x741b8cd7,
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.initial = 0xffffffff,
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.reflect_input = true,
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.reflect_output = true,
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.xor_output = 0xffffffff,
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});
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pub const Crc32Mef = Crc(u32, .{
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.polynomial = 0x741b8cd7,
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.initial = 0xffffffff,
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@ -1,11 +1,5 @@
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// There is a generic CRC implementation "Crc()" which can be paramterized via
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// the Algorithm struct for a plethora of uses, along with two implementations
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// of CRC32 implemented with the following key characteristics:
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//
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// - Crc32WithPoly uses 8Kb of tables but is ~10x faster than the small method.
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//
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// - Crc32SmallWithPoly uses only 64 bytes of memory but is slower. Be aware that this is
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// still moderately fast just slow relative to the slicing approach.
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// the Algorithm struct for a plethora of uses.
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//
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// The primary interface for all of the standard CRC algorithms is the
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// generated file "crc.zig", which uses the implementation code here to define
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@ -108,134 +102,11 @@ pub fn Crc(comptime W: type, comptime algorithm: Algorithm(W)) type {
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}
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pub const Polynomial = enum(u32) {
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IEEE = 0xedb88320,
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Castagnoli = 0x82f63b78,
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Koopman = 0xeb31d82e,
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IEEE = @compileError("use Crc with algorithm .Crc32IsoHdlc"),
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Castagnoli = @compileError("use Crc with algorithm .Crc32Iscsi"),
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Koopman = @compileError("use Crc with algorithm .Crc32Koopman"),
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_,
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};
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// slicing-by-8 crc32 implementation.
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pub fn Crc32WithPoly(comptime poly: Polynomial) type {
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return struct {
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const Self = @This();
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const lookup_tables = block: {
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@setEvalBranchQuota(20000);
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var tables: [8][256]u32 = undefined;
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for (&tables[0], 0..) |*e, i| {
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var crc = @as(u32, @intCast(i));
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var j: usize = 0;
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while (j < 8) : (j += 1) {
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if (crc & 1 == 1) {
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crc = (crc >> 1) ^ @intFromEnum(poly);
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} else {
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crc = (crc >> 1);
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}
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}
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e.* = crc;
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}
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var i: usize = 0;
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while (i < 256) : (i += 1) {
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var crc = tables[0][i];
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var j: usize = 1;
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while (j < 8) : (j += 1) {
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const index: u8 = @truncate(crc);
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crc = tables[0][index] ^ (crc >> 8);
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tables[j][i] = crc;
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}
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}
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break :block tables;
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};
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crc: u32,
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pub fn init() Self {
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return Self{ .crc = 0xffffffff };
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}
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pub fn update(self: *Self, input: []const u8) void {
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var i: usize = 0;
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while (i + 8 <= input.len) : (i += 8) {
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const p = input[i..][0..8];
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// Unrolling this way gives ~50Mb/s increase
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self.crc ^= std.mem.readInt(u32, p[0..4], .little);
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self.crc =
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lookup_tables[0][p[7]] ^
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lookup_tables[1][p[6]] ^
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lookup_tables[2][p[5]] ^
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lookup_tables[3][p[4]] ^
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lookup_tables[4][@as(u8, @truncate(self.crc >> 24))] ^
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lookup_tables[5][@as(u8, @truncate(self.crc >> 16))] ^
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lookup_tables[6][@as(u8, @truncate(self.crc >> 8))] ^
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lookup_tables[7][@as(u8, @truncate(self.crc >> 0))];
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}
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while (i < input.len) : (i += 1) {
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const index = @as(u8, @truncate(self.crc)) ^ input[i];
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self.crc = (self.crc >> 8) ^ lookup_tables[0][index];
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}
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}
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pub fn final(self: *Self) u32 {
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return ~self.crc;
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}
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pub fn hash(input: []const u8) u32 {
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var c = Self.init();
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c.update(input);
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return c.final();
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}
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};
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}
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// half-byte lookup table implementation.
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pub fn Crc32SmallWithPoly(comptime poly: Polynomial) type {
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return struct {
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const Self = @This();
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const lookup_table = block: {
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var table: [16]u32 = undefined;
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for (&table, 0..) |*e, i| {
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var crc = @as(u32, @intCast(i * 16));
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var j: usize = 0;
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while (j < 8) : (j += 1) {
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if (crc & 1 == 1) {
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crc = (crc >> 1) ^ @intFromEnum(poly);
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} else {
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crc = (crc >> 1);
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}
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}
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e.* = crc;
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}
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break :block table;
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};
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crc: u32,
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pub fn init() Self {
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return Self{ .crc = 0xffffffff };
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}
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pub fn update(self: *Self, input: []const u8) void {
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for (input) |b| {
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self.crc = lookup_table[@as(u4, @truncate(self.crc ^ (b >> 0)))] ^ (self.crc >> 4);
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self.crc = lookup_table[@as(u4, @truncate(self.crc ^ (b >> 4)))] ^ (self.crc >> 4);
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}
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}
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pub fn final(self: *Self) u32 {
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return ~self.crc;
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}
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pub fn hash(input: []const u8) u32 {
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var c = Self.init();
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c.update(input);
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return c.final();
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}
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};
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}
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pub const Crc32WithPoly = @compileError("use Crc instead");
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pub const Crc32SmallWithPoly = @compileError("use Crc instead");
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@ -5,22 +5,25 @@ const testing = std.testing;
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const verify = @import("../verify.zig");
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const crc = @import("../crc.zig");
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test "crc32 ieee" {
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inline for ([2]type{ crc.Crc32WithPoly(.IEEE), crc.Crc32SmallWithPoly(.IEEE) }) |ieee| {
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try testing.expect(ieee.hash("") == 0x00000000);
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try testing.expect(ieee.hash("a") == 0xe8b7be43);
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try testing.expect(ieee.hash("abc") == 0x352441c2);
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try verify.iterativeApi(ieee);
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}
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test "crc32 ieee regression" {
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const crc32 = crc.Crc32IsoHdlc;
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try testing.expectEqual(crc32.hash(""), 0x00000000);
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try testing.expectEqual(crc32.hash("a"), 0xe8b7be43);
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try testing.expectEqual(crc32.hash("abc"), 0x352441c2);
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}
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test "crc32 castagnoli" {
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inline for ([2]type{ crc.Crc32WithPoly(.Castagnoli), crc.Crc32SmallWithPoly(.Castagnoli) }) |casta| {
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try testing.expect(casta.hash("") == 0x00000000);
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try testing.expect(casta.hash("a") == 0xc1d04330);
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try testing.expect(casta.hash("abc") == 0x364b3fb7);
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try verify.iterativeApi(casta);
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}
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test "crc32 castagnoli regression" {
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const crc32 = crc.Crc32Iscsi;
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try testing.expectEqual(crc32.hash(""), 0x00000000);
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try testing.expectEqual(crc32.hash("a"), 0xc1d04330);
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try testing.expectEqual(crc32.hash("abc"), 0x364b3fb7);
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}
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test "crc32 koopman regression" {
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const crc32 = crc.Crc32Koopman;
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try testing.expectEqual(crc32.hash(""), 0x00000000);
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try testing.expectEqual(crc32.hash("a"), 0x0da2aa8a);
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try testing.expectEqual(crc32.hash("abc"), 0xba2322ac);
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}
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test "CRC-3/GSM" {
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@ -1134,6 +1137,17 @@ test "CRC-32/JAMCRC" {
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try testing.expectEqual(@as(u32, 0x340bc6d9), c.final());
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}
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test "CRC-32/KOOPMAN" {
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const Crc32Koopman = crc.Crc32Koopman;
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try testing.expectEqual(@as(u32, 0x2d3dd0ae), Crc32Koopman.hash("123456789"));
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var c = Crc32Koopman.init();
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c.update("1234");
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c.update("56789");
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try testing.expectEqual(@as(u32, 0x2d3dd0ae), c.final());
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}
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test "CRC-32/MEF" {
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const Crc32Mef = crc.Crc32Mef;
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@ -100,6 +100,7 @@ width=32 poly=0x04c11db7 init=0x00000000 refin=false refout=false xorout=0x
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width=32 poly=0x1edc6f41 init=0xffffffff refin=true refout=true xorout=0xffffffff check=0xe3069283 residue=0xb798b438 name="CRC-32/ISCSI"
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width=32 poly=0x04c11db7 init=0xffffffff refin=true refout=true xorout=0xffffffff check=0xcbf43926 residue=0xdebb20e3 name="CRC-32/ISO-HDLC"
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width=32 poly=0x04c11db7 init=0xffffffff refin=true refout=true xorout=0x00000000 check=0x340bc6d9 residue=0x00000000 name="CRC-32/JAMCRC"
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width=32 poly=0x741b8cd7 init=0xffffffff refin=true refout=true xorout=0xffffffff check=0x2d3dd0ae residue=0x00000000 name="CRC-32/KOOPMAN"
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width=32 poly=0x741b8cd7 init=0xffffffff refin=true refout=true xorout=0x00000000 check=0xd2c22f51 residue=0x00000000 name="CRC-32/MEF"
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width=32 poly=0x04c11db7 init=0xffffffff refin=false refout=false xorout=0x00000000 check=0x0376e6e7 residue=0x00000000 name="CRC-32/MPEG-2"
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width=32 poly=0x000000af init=0x00000000 refin=false refout=false xorout=0x00000000 check=0xbd0be338 residue=0x00000000 name="CRC-32/XFER"
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@ -48,8 +48,7 @@ pub fn main() anyerror!void {
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\\pub const Crc32WithPoly = impl.Crc32WithPoly;
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\\pub const Crc32SmallWithPoly = impl.Crc32SmallWithPoly;
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\\
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\\// IEEE is by far the most common CRC and so is aliased by default.
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\\pub const Crc32 = Crc32WithPoly(.IEEE);
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\\pub const Crc32 = Crc32IsoHdlc;
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\\
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\\test {
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\\ _ = @import("crc/test.zig");
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@ -72,22 +71,25 @@ pub fn main() anyerror!void {
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\\const verify = @import("../verify.zig");
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\\const crc = @import("../crc.zig");
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\\
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\\test "crc32 ieee" {
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\\ inline for ([2]type{ crc.Crc32WithPoly(.IEEE), crc.Crc32SmallWithPoly(.IEEE) }) |ieee| {
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\\ try testing.expect(ieee.hash("") == 0x00000000);
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\\ try testing.expect(ieee.hash("a") == 0xe8b7be43);
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\\ try testing.expect(ieee.hash("abc") == 0x352441c2);
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\\ try verify.iterativeApi(ieee);
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\\ }
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\\test "crc32 ieee regression" {
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\\ const crc32 = crc.Crc32IsoHdlc;
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\\ try testing.expectEqual(crc32.hash(""), 0x00000000);
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\\ try testing.expectEqual(crc32.hash("a"), 0xe8b7be43);
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\\ try testing.expectEqual(crc32.hash("abc"), 0x352441c2);
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\\}
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\\
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\\test "crc32 castagnoli" {
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\\ inline for ([2]type{ crc.Crc32WithPoly(.Castagnoli), crc.Crc32SmallWithPoly(.Castagnoli) }) |casta| {
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\\ try testing.expect(casta.hash("") == 0x00000000);
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\\ try testing.expect(casta.hash("a") == 0xc1d04330);
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\\ try testing.expect(casta.hash("abc") == 0x364b3fb7);
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\\ try verify.iterativeApi(casta);
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\\ }
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\\test "crc32 castagnoli regression" {
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\\ const crc32 = crc.Crc32Iscsi;
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\\ try testing.expectEqual(crc32.hash(""), 0x00000000);
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\\ try testing.expectEqual(crc32.hash("a"), 0xc1d04330);
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\\ try testing.expectEqual(crc32.hash("abc"), 0x364b3fb7);
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\\}
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\\
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\\test "crc32 koopman regression" {
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\\ const crc32 = crc.Koopman;
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\\ try testing.expectEqual(crc32.hash(""), 0x00000000);
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\\ try testing.expectEqual(crc32.hash("a"), 0x0da2aa8a);
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\\ try testing.expectEqual(crc32.hash("abc"), 0xba2322ac);
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\\}
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\\
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);
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