1 files changed, 368 insertions, 0 deletions

diff --git a/src/hashsig.c b/src/hashsig.c
new file mode 100644
index 000000000..3a75aaaed
--- /dev/null
+++ b/src/hashsig.c
@@ -0,0 +1,368 @@
+/*
+ * 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;
+}
+