mirror/zig
1
0
Fork 0
mirror of https://github.com/ziglang/zig.git synced 2026-01-05 21:13:24 +00:00
Code Issues Packages Projects Releases Wiki Activity

Create skipping table

Browse Source 
Also fallback to naive implementation if haystack is small
or if the needle is small or if sizeof type is not 1.
This commit is contained in:
dec05eba 2020-09-05 11:24:05 +02:00
parent 50c52e0135
commit e297b4815c
1 changed files with 55 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

72
lib/std/mem.zig
View File

@ -850,20 +850,56 @@ pub fn indexOfAnyPos(comptime T: type, slice: []const T, start_index: usize, val
pub fn indexOf(comptime T: type, haystack: []const T, needle: []const T) ?usize {
return indexOfPos(T, haystack, 0, needle);
}
/// 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;
var i: usize = haystack.len - needle.len;
while (true) : (i -= 1) {
if (mem.eql(T, haystack[i .. i + needle.len], needle)) return i;
if (i == 0) return null;
}
}
fn indexOfPosNaive(comptime T: type, haystack: []const T, start_index: usize, needle: []const T) ?usize {
if (needle.len > haystack.len) return null;
var i: usize = start_index;
const end = haystack.len - needle.len;
while (i <= end) : (i += 1) {
if (eql(T, haystack[i .. i + needle.len], needle)) return i;
}
return null;
}
fn boyerMooreHorspoolPreprocess(pattern: []const u8, table: []usize) void {
for (table) |*c| {
c.* = pattern.len;
}
var i: usize = 0;
while (i < pattern.len - 1) : (i += 1) {
table[pattern[i]] = pattern.len - 1 - i;
}
}
/// 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.
// Reverse boyer-moore-horspool algorithm
pub fn lastIndexOf(comptime T: type, haystack: []const T, needle: []const T) ?usize {
if (needle.len > haystack.len or needle.len == 0) return null;
if (T != u8 or haystack.len < 32 or needle.len <= 2)
return lastIndexOfNaive(T, haystack, needle);
var i: usize = needle.len - 1;
while (i < haystack.len) {
const reverseIndex = haystack.len - i - 1;
if (indexOfScalar(T, needle, haystack[reverseIndex])) |index| {
const haystackIndex = reverseIndex - index;
if (haystackIndex + needle.len <= haystack.len and mem.eql(T, haystack[haystackIndex .. haystackIndex + needle.len], needle)) return haystackIndex;
}
i += needle.len;
if (needle.len > haystack.len or needle.len == 0) return null;
var table: [256]usize = undefined;
boyerMooreHorspoolPreprocess(needle, table[0..]);
var i: usize = 0;
while (i <= haystack.len - needle.len) {
const reverseIndex = haystack.len - i - needle.len - 1;
if (mem.eql(T, haystack[reverseIndex .. reverseIndex + needle.len], needle)) return i;
i += table[haystack[reverseIndex + needle.len - 1]];
}
return null;
@ -871,15 +907,17 @@ 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 (needle.len > haystack.len or needle.len == 0) return null;
if (T != u8 or haystack.len < 32 or needle.len <= 2)
return indexOfPosNaive(T, haystack, start_index, needle);
var i: usize = start_index + needle.len - 1;
while (i < haystack.len) {
if (lastIndexOfScalar(T, needle, haystack[i])) |index| {
const haystackIndex = i - index;
if (haystackIndex + needle.len <= haystack.len and mem.eql(T, haystack[haystackIndex .. haystackIndex + needle.len], needle)) return haystackIndex;
}
i += needle.len;
if (needle.len > haystack.len or needle.len == 0) return null;
var table: [256]usize = undefined;
boyerMooreHorspoolPreprocess(needle, table[0..]);
var i: usize = start_index;
while (i <= haystack.len - needle.len) {
if (mem.eql(T, haystack[i .. i + needle.len], needle)) return i;
i += table[haystack[i + needle.len - 1]];
}
return null;