thodg/libgit2

diff --git a/Makefile b/Makefile
index 4063e6c..850cf44 100644
--- a/Makefile
+++ b/Makefile
@@ -98,7 +98,7 @@ $(TEST_EXE): tests/%.exe: tests/%.o tests/%_main.o
 	$(CC) -o $@ \
 		$(patsubst %.exe,%_main.o,$@) \
 		$(patsubst %.exe,%.o,$@) \
-		$(T_LIB) -L. -lgit2 -lz
+		$(T_LIB) -L. -lgit2 -lz -lcrypto
 
 $(TEST_RUN): tests/%.run: tests/%.exe
 	@t=trash-$(<F) && \
diff --git a/src/hash.c b/src/hash.c
new file mode 100644
index 0000000..4ff1dd0
--- /dev/null
+++ b/src/hash.c
@@ -0,0 +1,87 @@
+/*
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License, version 2,
+ * as published by the Free Software Foundation.
+ *
+ * In addition to the permissions in the GNU General Public License,
+ * the authors give you unlimited permission to link the compiled
+ * version of this file into combinations with other programs,
+ * and to distribute those combinations without any restriction
+ * coming from the use of this file.  (The General Public License
+ * restrictions do apply in other respects; for example, they cover
+ * modification of the file, and distribution when not linked into
+ * a combined executable.)
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; see the file COPYING.  If not, write to
+ * the Free Software Foundation, 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#include "common.h"
+#include "hash.h"
+#include <openssl/sha.h>
+
+struct git_hash_ctx {
+	SHA_CTX c;
+};
+
+git_hash_ctx *git_hash_new_ctx(void)
+{
+	git_hash_ctx *ctx = malloc(sizeof(*ctx));
+
+	if (!ctx)
+		return NULL;
+
+	SHA1_Init(&ctx->c);
+
+	return ctx;
+}
+
+void git_hash_free_ctx(git_hash_ctx *ctx)
+{
+	free(ctx);
+}
+
+void git_hash_init(git_hash_ctx *ctx)
+{
+	assert(ctx);
+	SHA1_Init(&ctx->c);
+}
+
+void git_hash_update(git_hash_ctx *ctx, const void *data, size_t len)
+{
+	assert(ctx);
+	SHA1_Update(&ctx->c, data, len);
+}
+
+void git_hash_final(git_oid *out, git_hash_ctx *ctx)
+{
+	assert(ctx);
+	SHA1_Final(out->id, &ctx->c);
+}
+
+void git_hash_buf(git_oid *out, const void *data, size_t len)
+{
+	SHA_CTX c;
+
+	SHA1_Init(&c);
+	SHA1_Update(&c, data, len);
+	SHA1_Final(out->id, &c);
+}
+
+void git_hash_vec(git_oid *out, git_buf_vec *vec, size_t n)
+{
+	SHA_CTX c;
+	size_t i;
+
+	SHA1_Init(&c);
+	for (i = 0; i < n; i++)
+		SHA1_Update(&c, vec[i].data, vec[i].len);
+	SHA1_Final(out->id, &c);
+}
diff --git a/src/hash.h b/src/hash.h
new file mode 100644
index 0000000..b371c05
--- /dev/null
+++ b/src/hash.h
@@ -0,0 +1,26 @@
+/*
+ * hash.h
+ */
+#ifndef INCLUDE_hash_h__
+#define INCLUDE_hash_h__
+
+#include "git/oid.h"
+
+typedef struct git_hash_ctx git_hash_ctx;
+
+typedef struct {
+	void *data;
+	size_t len;
+} git_buf_vec;
+
+git_hash_ctx *git_hash_new_ctx(void);
+void git_hash_free_ctx(git_hash_ctx *ctx);
+
+void git_hash_init(git_hash_ctx *c);
+void git_hash_update(git_hash_ctx *c, const void *data, size_t len);
+void git_hash_final(git_oid *out, git_hash_ctx *c);
+
+void git_hash_buf(git_oid *out, const void *data, size_t len);
+void git_hash_vec(git_oid *out, git_buf_vec *vec, size_t n);
+
+#endif /* INCLUDE_hash_h__ */
diff --git a/tests/t0000-hash.c b/tests/t0000-hash.c
new file mode 100644
index 0000000..6e9df71
--- /dev/null
+++ b/tests/t0000-hash.c
@@ -0,0 +1,57 @@
+#include "test_lib.h"
+#include "hash.h"
+#include <git/oid.h>
+
+static char *hello_id = "22596363b3de40b06f981fb85d82312e8c0ed511";
+static char *hello_text = "hello world\n";
+
+static char *bye_id = "ce08fe4884650f067bd5703b6a59a8b3b3c99a09";
+static char *bye_text = "bye world\n";
+
+BEGIN_TEST(hash_iuf)
+    git_hash_ctx *ctx;
+    git_oid id1, id2;
+
+    must_be_true((ctx = git_hash_new_ctx()) != NULL);
+
+	/* should already be init'd */
+    git_hash_update(ctx, hello_text, strlen(hello_text));
+    git_hash_final(&id2, ctx);
+    must_pass(git_oid_mkstr(&id1, hello_id));
+    must_be_true(git_oid_cmp(&id1, &id2) == 0);
+
+	/* reinit should permit reuse */
+    git_hash_init(ctx);
+    git_hash_update(ctx, bye_text, strlen(bye_text));
+    git_hash_final(&id2, ctx);
+    must_pass(git_oid_mkstr(&id1, bye_id));
+    must_be_true(git_oid_cmp(&id1, &id2) == 0);
+
+    git_hash_free_ctx(ctx);
+END_TEST
+
+BEGIN_TEST(hash_buf)
+    git_oid id1, id2;
+
+    must_pass(git_oid_mkstr(&id1, hello_id));
+
+    git_hash_buf(&id2, hello_text, strlen(hello_text));
+
+    must_be_true(git_oid_cmp(&id1, &id2) == 0);
+END_TEST
+
+BEGIN_TEST(hash_vec)
+    git_oid id1, id2;
+    git_buf_vec vec[2];
+
+    must_pass(git_oid_mkstr(&id1, hello_id));
+
+    vec[0].data = hello_text;
+    vec[0].len  = 4;
+    vec[1].data = hello_text+4;
+    vec[1].len  = strlen(hello_text)-4;
+
+    git_hash_vec(&id2, vec, 2);
+
+    must_be_true(git_oid_cmp(&id1, &id2) == 0);
+END_TEST