From 43fd1e7b5a01623bc59fcf68254ce5be8e0b8d42 Mon Sep 17 00:00:00 2001
From: =?utf8?q?P=C3=A1draig=20Brady?=
Date: Mon, 11 Nov 2013 14:19:09 +0000
Subject: [PATCH] base64: provide a fast path for encoding well sized buffers
Avoid conditionals in the base64 encoding loop,
which was seen to give a 60% throughput improvement
with the base64 utility from coreutils:
$ truncate -s100MiB file.in
$ time base64-old -w0 < file.in >/dev/null
real 0m0.302s
$ time base64-new -w0 < file.in >/dev/null
real 0m0.182s
* lib/base64.c (base64_encode_fast): A new function to be called
when we don't want to NUL terminate, and we have enough space
in the output to encode the given input.
(base64_encode): Call the _fast() version when appropriate.
Also remove a redundant mask with 0x3F on the first encoded byte.
---
ChangeLog | 11 +++++++++++
lib/base64.c | 40 ++++++++++++++++++++++++++++++++++------
2 files changed, 45 insertions(+), 6 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 3ac439aa04..59de3e5730 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2013-11-11 Pádraig Brady
+
+ base64: provide a fast path for encoding well sized buffers
+ Avoid conditionals in the base64 encoding loop,
+ which was seen to give 60% better throughput.
+ * lib/base64.c (base64_encode_fast): A new function to be called
+ when we don't want to NUL terminate, and we have enough space
+ in the output to encode the given input.
+ (base64_encode): Call the _fast() version when appropriate.
+ Also remove a redundant mask with 0x3F on the first encoded byte.
+
2013-11-08 Paul Eggert
extern-inline: port better to OS X 10.9
diff --git a/lib/base64.c b/lib/base64.c
index 105f419b53..99c2d2e566 100644
--- a/lib/base64.c
+++ b/lib/base64.c
@@ -59,6 +59,27 @@ to_uchar (char ch)
return ch;
}
+static const char b64c[64] =
+ "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+/* Base64 encode IN array of size INLEN into OUT array. OUT needs
+ to be of length >= BASE64_LENGTH(INLEN), and INLEN needs to be
+ a multiple of 3. */
+static void
+base64_encode_fast (const char *restrict in, size_t inlen, char *restrict out)
+{
+ while (inlen)
+ {
+ *out++ = b64c[to_uchar (in[0]) >> 2];
+ *out++ = b64c[((to_uchar (in[0]) << 4) + (to_uchar (in[1]) >> 4)) & 0x3f];
+ *out++ = b64c[((to_uchar (in[1]) << 2) + (to_uchar (in[2]) >> 6)) & 0x3f];
+ *out++ = b64c[to_uchar (in[2]) & 0x3f];
+
+ inlen -= 3;
+ in += 3;
+ }
+}
+
/* Base64 encode IN array of size INLEN into OUT array of size OUTLEN.
If OUTLEN is less than BASE64_LENGTH(INLEN), write as many bytes as
possible. If OUTLEN is larger than BASE64_LENGTH(INLEN), also zero
@@ -67,28 +88,35 @@ void
base64_encode (const char *restrict in, size_t inlen,
char *restrict out, size_t outlen)
{
- static const char b64str[64] =
- "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+ /* Note this outlen constraint can be enforced at compile time.
+ I.E. that the output buffer is exactly large enough to hold
+ the encoded inlen bytes. The inlen constraints (of corresponding
+ to outlen, and being a multiple of 3) can change at runtime
+ at the end of input. However the common case when reading
+ large inputs is to have both constraints satisfied, so we depend
+ on both in base_encode_fast(). */
+ if (outlen % 4 == 0 && inlen == outlen / 4 * 3)
+ return base64_encode_fast (in, inlen, out);
while (inlen && outlen)
{
- *out++ = b64str[(to_uchar (in[0]) >> 2) & 0x3f];
+ *out++ = b64c[to_uchar (in[0]) >> 2];
if (!--outlen)
break;
- *out++ = b64str[((to_uchar (in[0]) << 4)
+ *out++ = b64c[((to_uchar (in[0]) << 4)
+ (--inlen ? to_uchar (in[1]) >> 4 : 0))
& 0x3f];
if (!--outlen)
break;
*out++ =
(inlen
- ? b64str[((to_uchar (in[1]) << 2)
+ ? b64c[((to_uchar (in[1]) << 2)
+ (--inlen ? to_uchar (in[2]) >> 6 : 0))
& 0x3f]
: '=');
if (!--outlen)
break;
- *out++ = inlen ? b64str[to_uchar (in[2]) & 0x3f] : '=';
+ *out++ = inlen ? b64c[to_uchar (in[2]) & 0x3f] : '=';
if (!--outlen)
break;
if (inlen)
--
2.39.5