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/*

* Copyright (C) the libgit2 contributors. All rights reserved.

*

* This file is part of libgit2, distributed under the GNU GPL v2 with

* a Linking Exception. For full terms see the included COPYING file.

*/

#include "hashsig.h"

#include "fileops.h"

#include "util.h"

typedef uint32_t hashsig_t;

typedef uint64_t hashsig_state;

#define HASHSIG_SCALE 100

#define HASHSIG_HASH_WINDOW 32

#define HASHSIG_HASH_START 0

#define HASHSIG_HASH_SHIFT 5

#define HASHSIG_HASH_MASK 0x7FFFFFFF

#define HASHSIG_HEAP_SIZE ((1 << 7) - 1)

typedef int (*hashsig_cmp)(const void *a, const void *b, void *);

typedef struct {

int size, asize;

hashsig_cmp cmp;

hashsig_t values[HASHSIG_HEAP_SIZE];

} hashsig_heap;

typedef struct {

hashsig_state state, shift_n;

char window[HASHSIG_HASH_WINDOW];

int win_len, win_pos, saw_lf;

} hashsig_in_progress;

#define HASHSIG_IN_PROGRESS_INIT { HASHSIG_HASH_START, 1, {0}, 0, 0, 1 }

struct git_hashsig {

hashsig_heap mins;

hashsig_heap maxs;

git_hashsig_option_t opt;

int considered;

};

#define HEAP_LCHILD_OF(I) (((I)*2)+1)

#define HEAP_RCHILD_OF(I) (((I)*2)+2)

#define HEAP_PARENT_OF(I) (((I)-1)>>1)

static void hashsig_heap_init(hashsig_heap *h, hashsig_cmp cmp)

{

h->size = 0;

h->asize = HASHSIG_HEAP_SIZE;

h->cmp = cmp;

}

static int hashsig_cmp_max(const void *a, const void *b, void *payload)

{

hashsig_t av = *(const hashsig_t *)a, bv = *(const hashsig_t *)b;

GIT_UNUSED(payload);

return (av < bv) ? -1 : (av > bv) ? 1 : 0;

}

static int hashsig_cmp_min(const void *a, const void *b, void *payload)

{

hashsig_t av = *(const hashsig_t *)a, bv = *(const hashsig_t *)b;

GIT_UNUSED(payload);

return (av > bv) ? -1 : (av < bv) ? 1 : 0;

}

static void hashsig_heap_up(hashsig_heap *h, int el)

{

int parent_el = HEAP_PARENT_OF(el);

while (el > 0 && h->cmp(&h->values[parent_el], &h->values[el], NULL) > 0) {

hashsig_t t = h->values[el];

h->values[el] = h->values[parent_el];

h->values[parent_el] = t;

el = parent_el;

parent_el = HEAP_PARENT_OF(el);

}

}

static void hashsig_heap_down(hashsig_heap *h, int el)

{

hashsig_t v, lv, rv;

/* 'el < h->size / 2' tests if el is bottom row of heap */

while (el < h->size / 2) {

int lel = HEAP_LCHILD_OF(el), rel = HEAP_RCHILD_OF(el), swapel;

v = h->values[el];

lv = h->values[lel];

rv = h->values[rel];

if (h->cmp(&v, &lv, NULL) < 0 && h->cmp(&v, &rv, NULL) < 0)

break;

swapel = (h->cmp(&lv, &rv, NULL) < 0) ? lel : rel;

h->values[el] = h->values[swapel];

h->values[swapel] = v;

el = swapel;

}

}

static void hashsig_heap_sort(hashsig_heap *h)

{

/* only need to do this at the end for signature comparison */

git__qsort_r(h->values, h->size, sizeof(hashsig_t), h->cmp, NULL);

}

static void hashsig_heap_insert(hashsig_heap *h, hashsig_t val)

{

/* if heap is full, pop top if new element should replace it */

if (h->size == h->asize && h->cmp(&val, &h->values[0], NULL) > 0) {

h->size--;

h->values[0] = h->values[h->size];

hashsig_heap_down(h, 0);

}

/* if heap is not full, insert new element */

if (h->size < h->asize) {

h->values[h->size++] = val;

hashsig_heap_up(h, h->size - 1);

}

}

GIT_INLINE(bool) hashsig_include_char(

char ch, git_hashsig_option_t opt, int *saw_lf)

{

if ((opt & GIT_HASHSIG_IGNORE_WHITESPACE) && git__isspace(ch))

return false;

if (opt & GIT_HASHSIG_SMART_WHITESPACE) {

if (ch == '\r' || (*saw_lf && git__isspace(ch)))

return false;

*saw_lf = (ch == '\n');

}

return true;

}

static void hashsig_initial_window(

git_hashsig *sig,

const char **data,

size_t size,

hashsig_in_progress *prog)

{

hashsig_state state, shift_n;

int win_len;

const char *scan, *end;

/* init until we have processed at least HASHSIG_HASH_WINDOW data */

if (prog->win_len >= HASHSIG_HASH_WINDOW)

return;

state = prog->state;

win_len = prog->win_len;

shift_n = prog->shift_n;

scan = *data;

end = scan + size;

while (scan < end && win_len < HASHSIG_HASH_WINDOW) {

char ch = *scan++;

if (!hashsig_include_char(ch, sig->opt, &prog->saw_lf))

continue;

state = (state * HASHSIG_HASH_SHIFT + ch) & HASHSIG_HASH_MASK;

if (!win_len)

shift_n = 1;

else

shift_n = (shift_n * HASHSIG_HASH_SHIFT) & HASHSIG_HASH_MASK;

prog->window[win_len++] = ch;

}

/* insert initial hash if we just finished */

if (win_len == HASHSIG_HASH_WINDOW) {

hashsig_heap_insert(&sig->mins, (hashsig_t)state);

hashsig_heap_insert(&sig->maxs, (hashsig_t)state);

sig->considered = 1;

}

prog->state = state;

prog->win_len = win_len;

prog->shift_n = shift_n;

*data = scan;

}

static int hashsig_add_hashes(

git_hashsig *sig,

const char *data,

size_t size,

hashsig_in_progress *prog)

{

const char *scan = data, *end = data + size;

hashsig_state state, shift_n, rmv;

if (prog->win_len < HASHSIG_HASH_WINDOW)

hashsig_initial_window(sig, &scan, size, prog);

state = prog->state;

shift_n = prog->shift_n;

/* advance window, adding new chars and removing old */

for (; scan < end; ++scan) {

char ch = *scan;

if (!hashsig_include_char(ch, sig->opt, &prog->saw_lf))

continue;

rmv = shift_n * prog->window[prog->win_pos];

state = (state - rmv) & HASHSIG_HASH_MASK;

state = (state * HASHSIG_HASH_SHIFT) & HASHSIG_HASH_MASK;

state = (state + ch) & HASHSIG_HASH_MASK;

hashsig_heap_insert(&sig->mins, (hashsig_t)state);

hashsig_heap_insert(&sig->maxs, (hashsig_t)state);

sig->considered++;

prog->window[prog->win_pos] = ch;

prog->win_pos = (prog->win_pos + 1) % HASHSIG_HASH_WINDOW;

}

prog->state = state;

return 0;

}

static int hashsig_finalize_hashes(git_hashsig *sig)

{

if (sig->mins.size < HASHSIG_HEAP_SIZE) {

giterr_set(GITERR_INVALID,

"File too small for similarity signature calculation");

return GIT_EBUFS;

}

hashsig_heap_sort(&sig->mins);

hashsig_heap_sort(&sig->maxs);

return 0;

}

static git_hashsig *hashsig_alloc(git_hashsig_option_t opts)

{

git_hashsig *sig = git__calloc(1, sizeof(git_hashsig));

if (!sig)

return NULL;

hashsig_heap_init(&sig->mins, hashsig_cmp_min);

hashsig_heap_init(&sig->maxs, hashsig_cmp_max);

sig->opt = opts;

return sig;

}

int git_hashsig_create(

git_hashsig **out,

const char *buf,

size_t buflen,

git_hashsig_option_t opts)

{

int error;

hashsig_in_progress prog = HASHSIG_IN_PROGRESS_INIT;

git_hashsig *sig = hashsig_alloc(opts);

GITERR_CHECK_ALLOC(sig);

error = hashsig_add_hashes(sig, buf, buflen, &prog);

if (!error)

error = hashsig_finalize_hashes(sig);

if (!error)

*out = sig;

else

git_hashsig_free(sig);

return error;

}

int git_hashsig_create_fromfile(

git_hashsig **out,

const char *path,

git_hashsig_option_t opts)

{

char buf[4096];

ssize_t buflen = 0;

int error = 0, fd;

hashsig_in_progress prog = HASHSIG_IN_PROGRESS_INIT;

git_hashsig *sig = hashsig_alloc(opts);

GITERR_CHECK_ALLOC(sig);

if ((fd = git_futils_open_ro(path)) < 0) {

git__free(sig);

return fd;

}

while (!error) {

if ((buflen = p_read(fd, buf, sizeof(buf))) <= 0) {

if ((error = (int)buflen) < 0)

giterr_set(GITERR_OS,

"Read error on '%s' calculating similarity hashes", path);

break;

}

error = hashsig_add_hashes(sig, buf, buflen, &prog);

}

p_close(fd);

if (!error)

error = hashsig_finalize_hashes(sig);

if (!error)

*out = sig;

else

git_hashsig_free(sig);

return error;

}

void git_hashsig_free(git_hashsig *sig)

{

git__free(sig);

}

static int hashsig_heap_compare(const hashsig_heap *a, const hashsig_heap *b)

{

int matches = 0, i, j, cmp;

assert(a->cmp == b->cmp);

/* hash heaps are sorted - just look for overlap vs total */

for (i = 0, j = 0; i < a->size && j < b->size; ) {

cmp = a->cmp(&a->values[i], &b->values[j], NULL);

if (cmp < 0)

++i;

else if (cmp > 0)

++j;

else {

++i; ++j; ++matches;

}

}

return HASHSIG_SCALE * (matches * 2) / (a->size + b->size);

}

int git_hashsig_compare(const git_hashsig *a, const git_hashsig *b)

{

return (hashsig_heap_compare(&a->mins, &b->mins) +

hashsig_heap_compare(&a->maxs, &b->maxs)) / 2;

}