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Commit 805ebef

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aqrlnItalo A. Casas
aqrln
authored and
Italo A. Casas
committed
buffer: optimize decoding wrapped base64 data
The fast base64 decoder used to switch to the slow one permanently when it saw a whitespace or other garbage character. Since the most common situation such characters may be encountered in is line-wrapped base64 data, a more profitable strategy is to decode a single 24-bit group with the slow decoder and then continue running the fast algorithm. PR-URL: #12146 Ref: #12114 Reviewed-By: Anna Henningsen <anna@addaleax.net> Reviewed-By: Trevor Norris <trev.norris@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>
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‎benchmark/buffers/buffer-base64-decode-wrapped.js‎

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+26Lines changed: 26 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,26 @@
1+
'use strict';
2+
3+
const common = require('../common.js');
4+
5+
const bench = common.createBenchmark(main, {
6+
n: [32],
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});
8+
9+
function main(conf) {
10+
const n = +conf.n;
11+
const charsPerLine = 76;
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const linesCount = 8 << 16;
13+
const bytesCount = charsPerLine * linesCount / 4 * 3;
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const line = 'abcd'.repeat(charsPerLine / 4) + '\n';
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const data = line.repeat(linesCount);
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// eslint-disable-next-line no-unescaped-regexp-dot
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data.match(/./); // Flatten the string
19+
const buffer = Buffer.alloc(bytesCount, line, 'base64');
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bench.start();
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for (var i = 0; i < n; i++) {
23+
buffer.base64Write(data, 0, bytesCount);
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}
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bench.end(n);
26+
}
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‎src/base64.h‎

Copy file name to clipboardExpand all lines: src/base64.h
+35-34Lines changed: 35 additions & 34 deletions
Original file line numberDiff line numberDiff line change
@@ -52,36 +52,33 @@ extern const int8_t unbase64_table[256];
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5454
template <typename TypeName>
55-
size_t base64_decode_slow(char* dst, size_t dstlen,
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const TypeName* src, size_t srclen) {
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bool base64_decode_group_slow(char* const dst, const size_t dstlen,
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const TypeName* const src, const size_t srclen,
57+
size_t* const i, size_t* const k) {
5758
uint8_t hi;
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uint8_t lo;
59-
size_t i = 0;
60-
size_t k = 0;
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for (;;) {
6260
#define V(expr) \
63-
for (;;) { \
64-
const uint8_t c = src[i]; \
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lo = unbase64(c); \
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i += 1; \
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if (lo < 64) \
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break; /* Legal character. */ \
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if (c == '=' || i >= srclen) \
70-
return k; \
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} \
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expr; \
73-
if (i >= srclen) \
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return k; \
75-
if (k >= dstlen) \
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return k; \
77-
hi = lo;
78-
V(/* Nothing. */);
79-
V(dst[k++] = ((hi & 0x3F) << 2) | ((lo & 0x30) >> 4));
80-
V(dst[k++] = ((hi & 0x0F) << 4) | ((lo & 0x3C) >> 2));
81-
V(dst[k++] = ((hi & 0x03) << 6) | ((lo & 0x3F) >> 0));
61+
for (;;) { \
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const uint8_t c = src[*i]; \
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lo = unbase64(c); \
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*i += 1; \
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if (lo < 64) \
66+
break; /* Legal character. */ \
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if (c == '=' || *i >= srclen) \
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return false; /* Stop decoding. */ \
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} \
70+
expr; \
71+
if (*i >= srclen) \
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return false; \
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if (*k >= dstlen) \
74+
return false; \
75+
hi = lo;
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V(/* Nothing. */);
77+
V(dst[(*k)++] = ((hi & 0x3F) << 2) | ((lo & 0x30) >> 4));
78+
V(dst[(*k)++] = ((hi & 0x0F) << 4) | ((lo & 0x3C) >> 2));
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V(dst[(*k)++] = ((hi & 0x03) << 6) | ((lo & 0x3F) >> 0));
8280
#undef V
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}
84-
UNREACHABLE();
81+
return true; // Continue decoding.
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}
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@@ -90,8 +87,8 @@ size_t base64_decode_fast(char* const dst, const size_t dstlen,
9087
const TypeName* const src, const size_t srclen,
9188
const size_t decoded_size) {
9289
const size_t available = dstlen < decoded_size ? dstlen : decoded_size;
93-
const size_t max_i = srclen / 4 * 4;
9490
const size_t max_k = available / 3 * 3;
91+
size_t max_i = srclen / 4 * 4;
9592
size_t i = 0;
9693
size_t k = 0;
9794
while (i < max_i && k < max_k) {
@@ -102,16 +99,20 @@ size_t base64_decode_fast(char* const dst, const size_t dstlen,
10299
unbase64(src[i + 3]);
103100
// If MSB is set, input contains whitespace or is not valid base64.
104101
if (v & 0x80808080) {
105-
break;
102+
const size_t old_i = i;
103+
if (!base64_decode_group_slow(dst, dstlen, src, srclen, &i, &k))
104+
return k;
105+
max_i = old_i + (srclen - i) / 4 * 4; // Align max_i again.
106+
} else {
107+
dst[k + 0] = ((v >> 22) & 0xFC) | ((v >> 20) & 0x03);
108+
dst[k + 1] = ((v >> 12) & 0xF0) | ((v >> 10) & 0x0F);
109+
dst[k + 2] = ((v >> 2) & 0xC0) | ((v >> 0) & 0x3F);
110+
i += 4;
111+
k += 3;
106112
}
107-
dst[k + 0] = ((v >> 22) & 0xFC) | ((v >> 20) & 0x03);
108-
dst[k + 1] = ((v >> 12) & 0xF0) | ((v >> 10) & 0x0F);
109-
dst[k + 2] = ((v >> 2) & 0xC0) | ((v >> 0) & 0x3F);
110-
i += 4;
111-
k += 3;
112113
}
113114
if (i < srclen && k < dstlen) {
114-
return k + base64_decode_slow(dst + k, dstlen - k, src + i, srclen - i);
115+
base64_decode_group_slow(dst, dstlen, src, srclen, &i, &k);
115116
}
116117
return k;
117118
}

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