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 3ac439aa0..59de3e573 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 105f419b5..99c2d2e56 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) -- 2.11.0