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Diffstat (limited to 'node_modules/@webassemblyjs/leb128/lib/bits.js')
-rw-r--r-- | node_modules/@webassemblyjs/leb128/lib/bits.js | 156 |
1 files changed, 156 insertions, 0 deletions
diff --git a/node_modules/@webassemblyjs/leb128/lib/bits.js b/node_modules/@webassemblyjs/leb128/lib/bits.js new file mode 100644 index 0000000..5acf246 --- /dev/null +++ b/node_modules/@webassemblyjs/leb128/lib/bits.js @@ -0,0 +1,156 @@ +// Copyright 2012 The Obvious Corporation. + +/* + * bits: Bitwise buffer utilities. The utilities here treat a buffer + * as a little-endian bigint, so the lowest-order bit is bit #0 of + * `buffer[0]`, and the highest-order bit is bit #7 of + * `buffer[buffer.length - 1]`. + */ + +/* + * Modules used + */ +"use strict"; +/* + * Exported bindings + */ + +/** + * Extracts the given number of bits from the buffer at the indicated + * index, returning a simple number as the result. If bits are requested + * that aren't covered by the buffer, the `defaultBit` is used as their + * value. + * + * The `bitLength` must be no more than 32. The `defaultBit` if not + * specified is taken to be `0`. + */ + +Object.defineProperty(exports, "__esModule", { + value: true +}); +exports.extract = extract; +exports.inject = inject; +exports.getSign = getSign; +exports.highOrder = highOrder; + +function extract(buffer, bitIndex, bitLength, defaultBit) { + if (bitLength < 0 || bitLength > 32) { + throw new Error("Bad value for bitLength."); + } + + if (defaultBit === undefined) { + defaultBit = 0; + } else if (defaultBit !== 0 && defaultBit !== 1) { + throw new Error("Bad value for defaultBit."); + } + + var defaultByte = defaultBit * 0xff; + var result = 0; // All starts are inclusive. The {endByte, endBit} pair is exclusive, but + // if endBit !== 0, then endByte is inclusive. + + var lastBit = bitIndex + bitLength; + var startByte = Math.floor(bitIndex / 8); + var startBit = bitIndex % 8; + var endByte = Math.floor(lastBit / 8); + var endBit = lastBit % 8; + + if (endBit !== 0) { + // `(1 << endBit) - 1` is the mask of all bits up to but not including + // the endBit. + result = get(endByte) & (1 << endBit) - 1; + } + + while (endByte > startByte) { + endByte--; + result = result << 8 | get(endByte); + } + + result >>>= startBit; + return result; + + function get(index) { + var result = buffer[index]; + return result === undefined ? defaultByte : result; + } +} +/** + * Injects the given bits into the given buffer at the given index. Any + * bits in the value beyond the length to set are ignored. + */ + + +function inject(buffer, bitIndex, bitLength, value) { + if (bitLength < 0 || bitLength > 32) { + throw new Error("Bad value for bitLength."); + } + + var lastByte = Math.floor((bitIndex + bitLength - 1) / 8); + + if (bitIndex < 0 || lastByte >= buffer.length) { + throw new Error("Index out of range."); + } // Just keeping it simple, until / unless profiling shows that this + // is a problem. + + + var atByte = Math.floor(bitIndex / 8); + var atBit = bitIndex % 8; + + while (bitLength > 0) { + if (value & 1) { + buffer[atByte] |= 1 << atBit; + } else { + buffer[atByte] &= ~(1 << atBit); + } + + value >>= 1; + bitLength--; + atBit = (atBit + 1) % 8; + + if (atBit === 0) { + atByte++; + } + } +} +/** + * Gets the sign bit of the given buffer. + */ + + +function getSign(buffer) { + return buffer[buffer.length - 1] >>> 7; +} +/** + * Gets the zero-based bit number of the highest-order bit with the + * given value in the given buffer. + * + * If the buffer consists entirely of the other bit value, then this returns + * `-1`. + */ + + +function highOrder(bit, buffer) { + var length = buffer.length; + var fullyWrongByte = (bit ^ 1) * 0xff; // the other-bit extended to a full byte + + while (length > 0 && buffer[length - 1] === fullyWrongByte) { + length--; + } + + if (length === 0) { + // Degenerate case. The buffer consists entirely of ~bit. + return -1; + } + + var byteToCheck = buffer[length - 1]; + var result = length * 8 - 1; + + for (var i = 7; i > 0; i--) { + if ((byteToCheck >> i & 1) === bit) { + break; + } + + result--; + } + + return result; +}
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