mirror/zig
1
0
Fork 0
mirror of https://github.com/ziglang/zig.git synced 2026-02-13 04:48:20 +00:00
Code Issues Packages Projects Releases Wiki Activity

Fix lastIndexOf and add tests that do not fallback to linear search

Browse Source 
Use sliceAsBytes to convert []const T to []const u8.
Cleanup.
This commit is contained in:
dec05eba 2020-09-05 14:17:38 +02:00
parent f65f3d24f8
commit a394a6300c
1 changed files with 41 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

69
lib/std/mem.zig
View File

@ -853,9 +853,7 @@ pub fn indexOf(comptime T: type, haystack: []const T, needle: []const T) ?usize
/// Find the index in a slice of a sub-slice, searching from the end backwards.
/// To start looking at a different index, slice the haystack first.
fn lastIndexOfNaive(comptime T: type, haystack: []const T, needle: []const T) ?usize {
if (needle.len > haystack.len) return null;
fn lastIndexOfLinear(comptime T: type, haystack: []const T, needle: []const T) ?usize {
var i: usize = haystack.len - needle.len;
while (true) : (i -= 1) {
if (mem.eql(T, haystack[i .. i + needle.len], needle)) return i;
@ -863,9 +861,7 @@ fn lastIndexOfNaive(comptime T: type, haystack: []const T, needle: []const T) ?u
}
}
fn indexOfPosNaive(comptime T: type, haystack: []const T, start_index: usize, needle: []const T) ?usize {
if (needle.len > haystack.len) return null;
fn indexOfPosLinear(comptime T: type, haystack: []const T, start_index: usize, needle: []const T) ?usize {
var i: usize = start_index;
const end = haystack.len - needle.len;
while (i <= end) : (i += 1) {
@ -874,6 +870,17 @@ fn indexOfPosNaive(comptime T: type, haystack: []const T, start_index: usize, ne
return null;
}
fn boyerMooreHorspoolPreprocessReverse(pattern: []const u8, table: []usize) void {
for (table) |*c| {
c.* = pattern.len;
}
var i: usize = pattern.len - 1;
while (i > 0) : (i -= 1) {
table[pattern[i]] = i;
}
}
fn boyerMooreHorspoolPreprocess(pattern: []const u8, table: []usize) void {
for (table) |*c| {
c.* = pattern.len;
@ -888,22 +895,23 @@ fn boyerMooreHorspoolPreprocess(pattern: []const u8, table: []usize) void {
/// To start looking at a different index, slice the haystack first.
// Reverse boyer-moore-horspool algorithm
pub fn lastIndexOf(comptime T: type, haystack: []const T, needle: []const T) ?usize {
if (!isValidAlign(T.bit_count) or haystack.len < 32 or needle.len <= 2)
return lastIndexOfNaive(T, haystack, needle);
if (needle.len > haystack.len or needle.len == 0) return null;
const haystackU8 = sliceAsBytes(haystack);
const needleU8 = sliceAsBytes(needle);
if (!isValidAlign(T.bit_count) or haystack.len < 32 or needle.len <= 2)
return lastIndexOfLinear(T, haystack, needle);
var table: [256]usize = undefined;
boyerMooreHorspoolPreprocess(needleU8, table[0..]);
const haystack_bytes = sliceAsBytes(haystack);
const needle_bytes = sliceAsBytes(needle);
var i: usize = 0;
while (i <= haystackU8.len - needleU8.len) {
const reverseIndex = haystackU8.len - i - needleU8.len - 1;
if (mem.eql(u8, haystackU8[reverseIndex .. reverseIndex + needleU8.len], needleU8)) return i;
i += table[haystackU8[reverseIndex + needleU8.len - 1]];
var skip_table: [256]usize = undefined;
boyerMooreHorspoolPreprocessReverse(needle_bytes, skip_table[0..]);
var i: usize = haystack_bytes.len - needle_bytes.len;
while (true) {
if (mem.eql(u8, haystack_bytes[i .. i + needle_bytes.len], needle_bytes)) return i;
const skip = skip_table[haystack_bytes[i]];
if (skip > i) break;
i -= skip;
}
return null;
@ -911,27 +919,32 @@ pub fn lastIndexOf(comptime T: type, haystack: []const T, needle: []const T) ?us
// Boyer-moore-horspool algorithm
pub fn indexOfPos(comptime T: type, haystack: []const T, start_index: usize, needle: []const T) ?usize {
if (!isValidAlign(T.bit_count) or haystack.len < 32 or needle.len <= 2)
return indexOfPosNaive(T, haystack, start_index, needle);
if (needle.len > haystack.len or needle.len == 0) return null;
const haystackU8 = sliceAsBytes(haystack);
const needleU8 = sliceAsBytes(needle);
if (!isValidAlign(T.bit_count) or haystack.len < 32 or needle.len <= 2)
return indexOfPosLinear(T, haystack, start_index, needle);
var table: [256]usize = undefined;
boyerMooreHorspoolPreprocess(needleU8, table[0..]);
const haystack_bytes = sliceAsBytes(haystack);
const needle_bytes = sliceAsBytes(needle);
var skip_table: [256]usize = undefined;
boyerMooreHorspoolPreprocess(needle_bytes, skip_table[0..]);
var i: usize = start_index;
while (i <= haystackU8.len - needleU8.len) {
if (mem.eql(u8, haystackU8[i .. i + needleU8.len], needleU8)) return i;
i += table[haystackU8[i + needleU8.len - 1]];
while (i <= haystack_bytes.len - needle_bytes.len) {
if (mem.eql(u8, haystack_bytes[i .. i + needle_bytes.len], needle_bytes)) return i;
i += skip_table[haystack_bytes[i + needle_bytes.len - 1]];
}
return null;
}
test "mem.indexOf" {
testing.expect(indexOf(u8, "one two three four five six seven eight nine ten", "three four").? == 8);
testing.expect(lastIndexOf(u8, "one two three four five six seven eight nine ten", "three four").? == 8);
testing.expect(indexOf(u8, "one two three four five six seven eight nine ten", "two two") == null);
testing.expect(lastIndexOf(u8, "one two three four five six seven eight nine ten", "two two") == null);
testing.expect(indexOf(u8, "one two three four", "four").? == 14);
testing.expect(lastIndexOf(u8, "one two three two four", "two").? == 14);
testing.expect(indexOf(u8, "one two three four", "gour") == null);