69 lines
1.4 KiB
JavaScript
69 lines
1.4 KiB
JavaScript
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/* Wrapper for accessing strings through sequential reads */
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function Stream(str) {
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var position = 0;
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function read(length) {
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var result = str.substr(position, length);
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position += length;
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return result;
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}
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/* read a big-endian 32-bit integer */
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function readInt32() {
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var result = (
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(str.charCodeAt(position) << 24)
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+ (str.charCodeAt(position + 1) << 16)
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+ (str.charCodeAt(position + 2) << 8)
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+ str.charCodeAt(position + 3));
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position += 4;
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return result;
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}
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/* read a big-endian 16-bit integer */
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function readInt16() {
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var result = (
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(str.charCodeAt(position) << 8)
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+ str.charCodeAt(position + 1));
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position += 2;
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return result;
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}
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/* read an 8-bit integer */
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function readInt8(signed) {
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var result = str.charCodeAt(position);
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if (signed && result > 127) result -= 256;
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position += 1;
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return result;
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}
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function eof() {
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return position >= str.length;
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}
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/* read a MIDI-style variable-length integer
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(big-endian value in groups of 7 bits,
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with top bit set to signify that another byte follows)
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*/
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function readVarInt() {
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var result = 0;
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while (true) {
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var b = readInt8();
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if (b & 0x80) {
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result += (b & 0x7f);
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result <<= 7;
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} else {
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/* b is the last byte */
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return result + b;
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}
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}
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}
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return {
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'eof': eof,
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'read': read,
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'readInt32': readInt32,
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'readInt16': readInt16,
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'readInt8': readInt8,
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'readVarInt': readVarInt
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}
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}
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