1 // Copyright 2019 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #include <climits>
6 #include <limits>
7
8 #include "src/base/logging.h"
9 #include "src/base/vlq-base64.h"
10
11 namespace v8 {
12 namespace base {
13
14 namespace {
15 constexpr int8_t kCharToDigit[] = {
16 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
17 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
18 -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
19 -1, -1, -1, -1, -1, -1, -1, 0x3e, -1, -1, -1, 0x3f,
20 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, -1, -1,
21 -1, -1, -1, -1, -1, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06,
22 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x10, 0x11, 0x12,
23 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, -1, -1, -1, -1, -1,
24 -1, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, 0x21, 0x22, 0x23, 0x24,
25 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30,
26 0x31, 0x32, 0x33, -1, -1, -1, -1, -1};
27
28 constexpr uint32_t kContinueShift = 5;
29 constexpr uint32_t kContinueMask = 1 << kContinueShift;
30 constexpr uint32_t kDataMask = kContinueMask - 1;
31
charToDigitDecode(uint8_t c)32 int8_t charToDigitDecode(uint8_t c) { return c < 128u ? kCharToDigit[c] : -1; }
33 } // namespace
34
charToDigitDecodeForTesting(uint8_t c)35 int8_t charToDigitDecodeForTesting(uint8_t c) { return charToDigitDecode(c); }
36
VLQBase64Decode(const char * start,size_t sz,size_t * pos)37 int32_t VLQBase64Decode(const char* start, size_t sz, size_t* pos) {
38 uint32_t res = 0;
39 uint64_t shift = 0;
40 int32_t digit;
41
42 do {
43 if (*pos >= sz) {
44 return std::numeric_limits<int32_t>::min();
45 }
46 digit = static_cast<int>(charToDigitDecode(start[*pos]));
47 bool is_last_byte = (shift + kContinueShift >= 32);
48 if (digit == -1 || (is_last_byte && (digit >> 2) != 0)) {
49 return std::numeric_limits<int32_t>::min();
50 }
51 res += (digit & kDataMask) << shift;
52 shift += kContinueShift;
53 (*pos)++;
54 } while (digit & kContinueMask);
55 return (res & 1) ? -static_cast<int32_t>(res >> 1) : (res >> 1);
56 }
57 } // namespace base
58 } // namespace v8
59