From: Andre Noll <maan@systemlinux.org>
Date: Mon, 25 Mar 2013 19:05:05 +0000 (+0000)
Subject: string: Speed up xvasprintf().
X-Git-Tag: v0.4.13~33^2
X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=commitdiff_plain;h=bf1831886b93258ffcec63c47d6737fffff53aae;ds=sidebyside

string: Speed up xvasprintf().

This avoids to call vsnprintf() twice in the common case where the
result is small.

The running time of a simple test case that called this function in
a loop improved from 13s to 8s due to this change.
---

diff --git a/string.c b/string.c
index ba744bff..4d8b8b74 100644
--- a/string.c
+++ b/string.c
@@ -136,15 +136,18 @@ __must_check __malloc char *para_strdup(const char *s)
 __printf_2_0 unsigned xvasprintf(char **result, const char *fmt, va_list ap)
 {
 	int ret;
-	size_t size;
+	size_t size = 150;
 	va_list aq;
 
+	*result = para_malloc(size + 1);
 	va_copy(aq, ap);
-	ret = vsnprintf(NULL, 0, fmt, aq);
+	ret = vsnprintf(*result, size, fmt, aq);
 	va_end(aq);
 	assert(ret >= 0);
+	if (ret < size) /* OK */
+		return ret;
 	size = ret + 1;
-	*result = para_malloc(size);
+	*result = para_realloc(*result, size);
 	va_copy(aq, ap);
 	ret = vsnprintf(*result, size, fmt, aq);
 	va_end(aq);