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optimize KMP search in CCString.Find (hand-specialize code)

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This commit is contained in:
Simon Cruanes 2016-03-20 23:20:46 +01:00
parent 71794d8d45
commit 5e30104954
1 changed files with 37 additions and 14 deletions
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51
src/core/CCString.cppo.ml
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@ -134,17 +134,14 @@ module Find = struct
[i] index in [s]
[j] index in [pattern]
[len] length of [s] *)
let kmp_find_
: type a. dir:a direction -> pattern:a kmp_pattern -> string -> int -> int
= fun ~dir ~pattern s idx ->
let kmp_find ~pattern s idx =
let len = length s in
let get = get_ ~dir in
let i = ref idx in
let j = ref 0 in
let pat_len = kmp_pattern_length pattern in
while !j < pat_len && !i + !j < len do
let c = get s (!i + !j) in
let expected = get pattern.str !j in
let c = String.get s (!i + !j) in
let expected = String.get pattern.str !j in
if c = expected
then (
(* char matches *)
@ -168,18 +165,44 @@ module Find = struct
then !i
else -1
let kmp_find ~pattern s i = kmp_find_ ~dir:Direct ~pattern s i
let kmp_rfind ~pattern s i =
let i = String.length s - i - 1 in
let res = kmp_find_ ~dir:Reverse ~pattern s i in
(* proper search function, from the right.
[i] index in [s]
[j] index in [pattern]
[len] length of [s] *)
let kmp_rfind ~pattern s idx =
let len = length s in
let i = ref (len - idx - 1) in
let j = ref 0 in
let pat_len = kmp_pattern_length pattern in
while !j < pat_len && !i + !j < len do
let c = String.get s (len - !i - !j - 1) in
let expected = String.get pattern.str (String.length pattern.str - !j - 1) in
if c = expected
then (
(* char matches *)
incr j;
) else (
let fail_offset = pattern.failure.(!j) in
if fail_offset >= 0
then (
assert (fail_offset < !j);
(* follow the failure link *)
i := !i + !j - fail_offset;
j := fail_offset
) else (
(* beginning of pattern *)
j := 0;
incr i
)
)
done;
(* adjust result: first, [res = string.length s - res -1] to convert
back to real indices; then, what we got is actually the position
of the end of the pattern, so we subtract the [length of the pattern -1]
to obtain the real result. *)
if res = ~-1
then res
else (String.length s - res) - kmp_pattern_length pattern
if !j = pat_len
then len - !i - kmp_pattern_length pattern
else -1
type 'a pattern =
| P_char of char