Ben Murdoch | c561043 | 2016-08-08 18:44:38 +0100 | [diff] [blame^] | 1 | // Copyright 2016 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 | #ifndef V8_WASM_LEB_HELPER_H_ |
| 6 | #define V8_WASM_LEB_HELPER_H_ |
| 7 | |
| 8 | namespace v8 { |
| 9 | namespace internal { |
| 10 | namespace wasm { |
| 11 | |
| 12 | class LEBHelper { |
| 13 | public: |
| 14 | // Write a 32-bit unsigned LEB to {dest}, updating {dest} to point after |
| 15 | // the last uint8_t written. No safety checks. |
| 16 | static void write_u32v(uint8_t** dest, uint32_t val) { |
| 17 | while (val >= 0x80) { |
| 18 | *((*dest)++) = static_cast<uint8_t>(0x80 | (val & 0x7F)); |
| 19 | val >>= 7; |
| 20 | } |
| 21 | *((*dest)++) = static_cast<uint8_t>(val & 0x7F); |
| 22 | } |
| 23 | |
| 24 | // Write a 32-bit signed LEB to {dest}, updating {dest} to point after |
| 25 | // the last uint8_t written. No safety checks. |
| 26 | static void write_i32v(uint8_t** dest, int32_t val) { |
| 27 | if (val >= 0) { |
| 28 | while (val >= 0x40) { // prevent sign extension. |
| 29 | *((*dest)++) = static_cast<uint8_t>(0x80 | (val & 0x7F)); |
| 30 | val >>= 7; |
| 31 | } |
| 32 | *((*dest)++) = static_cast<uint8_t>(val & 0xFF); |
| 33 | } else { |
| 34 | while ((val >> 6) != -1) { |
| 35 | *((*dest)++) = static_cast<uint8_t>(0x80 | (val & 0x7F)); |
| 36 | val >>= 7; |
| 37 | } |
| 38 | *((*dest)++) = static_cast<uint8_t>(val & 0x7F); |
| 39 | } |
| 40 | } |
| 41 | |
| 42 | // Write a 64-bit unsigned LEB to {dest}, updating {dest} to point after |
| 43 | // the last uint8_t written. No safety checks. |
| 44 | static void write_u64v(uint8_t** dest, uint64_t val) { |
| 45 | while (val >= 0x80) { |
| 46 | *((*dest)++) = static_cast<uint8_t>(0x80 | (val & 0x7F)); |
| 47 | val >>= 7; |
| 48 | } |
| 49 | *((*dest)++) = static_cast<uint8_t>(val & 0x7F); |
| 50 | } |
| 51 | |
| 52 | // Write a 64-bit signed LEB to {dest}, updating {dest} to point after |
| 53 | // the last uint8_t written. No safety checks. |
| 54 | static void write_i64v(uint8_t** dest, int64_t val) { |
| 55 | if (val >= 0) { |
| 56 | while (val >= 0x40) { // prevent sign extension. |
| 57 | *((*dest)++) = static_cast<uint8_t>(0x80 | (val & 0x7F)); |
| 58 | val >>= 7; |
| 59 | } |
| 60 | *((*dest)++) = static_cast<uint8_t>(val & 0xFF); |
| 61 | } else { |
| 62 | while ((val >> 6) != -1) { |
| 63 | *((*dest)++) = static_cast<uint8_t>(0x80 | (val & 0x7F)); |
| 64 | val >>= 7; |
| 65 | } |
| 66 | *((*dest)++) = static_cast<uint8_t>(val & 0x7F); |
| 67 | } |
| 68 | } |
| 69 | |
| 70 | // TODO(titzer): move core logic for decoding LEBs from decoder.h to here. |
| 71 | |
| 72 | // Compute the size of {val} if emitted as an LEB32. |
| 73 | static inline size_t sizeof_u32v(size_t val) { |
| 74 | size_t size = 0; |
| 75 | do { |
| 76 | size++; |
| 77 | val = val >> 7; |
| 78 | } while (val > 0); |
| 79 | return size; |
| 80 | } |
| 81 | |
| 82 | // Compute the size of {val} if emitted as an LEB32. |
| 83 | static inline size_t sizeof_i32v(int32_t val) { |
| 84 | size_t size = 1; |
| 85 | if (val >= 0) { |
| 86 | while (val >= 0x40) { // prevent sign extension. |
| 87 | size++; |
| 88 | val >>= 7; |
| 89 | } |
| 90 | } else { |
| 91 | while ((val >> 6) != -1) { |
| 92 | size++; |
| 93 | val >>= 7; |
| 94 | } |
| 95 | } |
| 96 | return size; |
| 97 | } |
| 98 | |
| 99 | // Compute the size of {val} if emitted as an unsigned LEB64. |
| 100 | static inline size_t sizeof_u64v(uint64_t val) { |
| 101 | size_t size = 0; |
| 102 | do { |
| 103 | size++; |
| 104 | val = val >> 7; |
| 105 | } while (val > 0); |
| 106 | return size; |
| 107 | } |
| 108 | |
| 109 | // Compute the size of {val} if emitted as a signed LEB64. |
| 110 | static inline size_t sizeof_i64v(int64_t val) { |
| 111 | size_t size = 1; |
| 112 | if (val >= 0) { |
| 113 | while (val >= 0x40) { // prevent sign extension. |
| 114 | size++; |
| 115 | val >>= 7; |
| 116 | } |
| 117 | } else { |
| 118 | while ((val >> 6) != -1) { |
| 119 | size++; |
| 120 | val >>= 7; |
| 121 | } |
| 122 | } |
| 123 | return size; |
| 124 | } |
| 125 | }; |
| 126 | |
| 127 | } // namespace wasm |
| 128 | } // namespace internal |
| 129 | } // namespace v8 |
| 130 | |
| 131 | #endif // V8_WASM_LEB_HELPER_H_ |