reftable: utility functions

This commit provides basic utility classes for the reftable library.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

reftable/basics.c

@@ -0,0 +1,128 @@
+/*
+Copyright 2020 Google LLC
+
+Use of this source code is governed by a BSD-style
+license that can be found in the LICENSE file or at
+https://developers.google.com/open-source/licenses/bsd
+*/
+
+#include "basics.h"
+
+void put_be24(uint8_t *out, uint32_t i)
+{
+	out[0] = (uint8_t)((i >> 16) & 0xff);
+	out[1] = (uint8_t)((i >> 8) & 0xff);
+	out[2] = (uint8_t)(i & 0xff);
+}
+
+uint32_t get_be24(uint8_t *in)
+{
+	return (uint32_t)(in[0]) << 16 | (uint32_t)(in[1]) << 8 |
+	       (uint32_t)(in[2]);
+}
+
+void put_be16(uint8_t *out, uint16_t i)
+{
+	out[0] = (uint8_t)((i >> 8) & 0xff);
+	out[1] = (uint8_t)(i & 0xff);
+}
+
+int binsearch(size_t sz, int (*f)(size_t k, void *args), void *args)
+{
+	size_t lo = 0;
+	size_t hi = sz;
+
+	/* Invariants:
+	 *
+	 *  (hi == sz) || f(hi) == true
+	 *  (lo == 0 && f(0) == true) || fi(lo) == false
+	 */
+	while (hi - lo > 1) {
+		size_t mid = lo + (hi - lo) / 2;
+
+		if (f(mid, args))
+			hi = mid;
+		else
+			lo = mid;
+	}
+
+	if (lo)
+		return hi;
+
+	return f(0, args) ? 0 : 1;
+}
+
+void free_names(char **a)
+{
+	char **p;
+	if (!a) {
+		return;
+	}
+	for (p = a; *p; p++) {
+		reftable_free(*p);
+	}
+	reftable_free(a);
+}
+
+int names_length(char **names)
+{
+	char **p = names;
+	for (; *p; p++) {
+		/* empty */
+	}
+	return p - names;
+}
+
+void parse_names(char *buf, int size, char ***namesp)
+{
+	char **names = NULL;
+	size_t names_cap = 0;
+	size_t names_len = 0;
+
+	char *p = buf;
+	char *end = buf + size;
+	while (p < end) {
+		char *next = strchr(p, '\n');
+		if (next && next < end) {
+			*next = 0;
+		} else {
+			next = end;
+		}
+		if (p < next) {
+			if (names_len == names_cap) {
+				names_cap = 2 * names_cap + 1;
+				names = reftable_realloc(
+					names, names_cap * sizeof(*names));
+			}
+			names[names_len++] = xstrdup(p);
+		}
+		p = next + 1;
+	}
+
+	names = reftable_realloc(names, (names_len + 1) * sizeof(*names));
+	names[names_len] = NULL;
+	*namesp = names;
+}
+
+int names_equal(char **a, char **b)
+{
+	int i = 0;
+	for (; a[i] && b[i]; i++) {
+		if (strcmp(a[i], b[i])) {
+			return 0;
+		}
+	}
+
+	return a[i] == b[i];
+}
+
+int common_prefix_size(struct strbuf *a, struct strbuf *b)
+{
+	int p = 0;
+	for (; p < a->len && p < b->len; p++) {
+		if (a->buf[p] != b->buf[p])
+			break;
+	}
+
+	return p;
+}