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[PATCH] base64: provide a fast path for encoding well sized buffers
From: |
Pádraig Brady |
Subject: |
[PATCH] base64: provide a fast path for encoding well sized buffers |
Date: |
Mon, 11 Nov 2013 16:07:07 +0000 |
Avoid conditionals in the central 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 | 41 +++++++++++++++++++++++++++++++++++------
2 files changed, 46 insertions(+), 6 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index 3ac439a..2218aeb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2013-11-11 Pádraig Brady <address@hidden>
+
+ base64: provide a fast path for encoding well sized buffers
+ Avoid conditionals in the central 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 <address@hidden>
extern-inline: port better to OS X 10.9
diff --git a/lib/base64.c b/lib/base64.c
index 105f419..2bcf408 100644
--- a/lib/base64.c
+++ b/lib/base64.c
@@ -59,6 +59,27 @@ to_uchar (char ch)
return ch;
}
+/* 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)
+{
+ static const char b64c[64] =
+ "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+
+ 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 +88,36 @@ void
base64_encode (const char *restrict in, size_t inlen,
char *restrict out, size_t outlen)
{
- static const char b64str[64] =
+ static const char b64c[64] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
- while (inlen && outlen)
+ /* Note the outlen constraint can be enforced at compile time,
+ while the inlen can change at runtime at the end of input.
+ But the common case when reading large inputs is to have
+ both constraints satisfied, so we depend on both in
+ base_encode_fast(). */
+ if ((inlen % 3 == 0) && BASE64_LENGTH (inlen) == outlen)
+ return base64_encode_fast (in, inlen, out);
+
+ while (inlen)
{
- *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)
--
1.7.7.6
- [PATCH] base64: provide a fast path for encoding well sized buffers,
Pádraig Brady <=