bit-parser.js ➔ readBytesAsBits - Code Metrics - Inspection of "better float parsing" - rochars/byte-data - Measure and Improve Code Quality continuously with Scrutinizer

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Push — master ( b04473...f9e2c0 )

by Rafael S.

created 2017-12-06 23:36 UTC

bit-parser.js ➔ readBytesAsBits A

↳ Parent: src/bit-parser.js

Complexity

Conditions	2
Paths	2

Size

Total Lines

Duplication

Lines	0
Ratio	0 %

Importance

Changes	1
Bugs	0	Features	0

Metric	Value
cc	2
c	1
b	0
f	0
nc	2
dl	0
loc	10
rs	9.4285
nop	3

/**
 * bit-parser: Functions to read and write bytes.
 * Copyright (c) 2017 Rafael da Silva Rocha.
 * https://github.com/rochars/byte-data
 * Float32 based on int-bits: https://github.com/Jam3/int-bits
 */

let f32 = new Float32Array(1);
let i32 = new Int32Array(f32.buffer);


/**
 * Functions to read data from bytes.
 * @enum {Function}
 */
const BitReader = {

    /**
     * Read 1 8-bit int from from bytes.
     * @param {!Array<number>|Uint8Array} bytes An array of bytes.
     * @param {number} i The index to read.
     * @return {number}
     */
    "read8Bit": function (bytes, i) {
        return bytes[i];
    },

    /**
     * Read 1 16-bit int from from bytes.
     * @param {!Array<number>|Uint8Array} bytes An array of bytes.
     * @param {number} i The index to read.
     * @return {number}
     */
    "read16Bit": function (bytes, i) {
        return bytes[1 + i] << 8 | bytes[i];
    },

    /**
     * Read 1 16-bit float from from bytes.
     * Thanks https://stackoverflow.com/a/8796597
     * @param {!Array<number>|Uint8Array} bytes An array of bytes.
     * @param {number} i The index to read.
     * @return {number}
     */
    "read16BitFloat": function (bytes, i) {
        let binary = parseInt(getBinary([bytes[i], bytes[i+1]]), 2);
        let exponent = (binary & 0x7C00) >> 10;
        let fraction = binary & 0x03FF;
        let floatValue;
        if (exponent) {
            floatValue =  Math.pow(2, exponent - 15) * (1 + fraction / 0x400);
        } else {
            floatValue = 6.103515625e-5 * (fraction / 0x400);
        }
        return  floatValue * (binary >> 15 ? -1 : 1);
    },

    /**
     * Read 1 24-bit int from from bytes.
     * @param {!Array<number>|Uint8Array} bytes An array of bytes.
     * @param {number} i The index to read.
     * @return {number}
     */
    "read24Bit": function (bytes, i) {
        return bytes[2 + i] << 16 | BitReader["read16Bit"](bytes, i);
    },

    /**
     * Read 1 32-bit int from from bytes.
     * @param {!Array<number>|Uint8Array} bytes An array of bytes.
     * @param {number} i The index to read.
     * @return {number}
     */
    "read32Bit": function (bytes, i) {
        return (bytes[3 + i] << 24 |
            BitReader["read24Bit"](bytes, i)) >>> 0;
    },

    /**
     * Read 1 32-bit float from from bytes.
     * @param {!Array<number>|Uint8Array} bytes An array of bytes.
     * @param {number} i The index to read.
     * @return {number}
     */
    "read32BitFloat": function (bytes, i) {
        i32[0] = BitReader["read32Bit"](bytes, i);
        return f32[0];
    },

    /**
     * Read 1 40-bit int from from bytes.
     * @param {!Array<number>|Uint8Array} bytes An array of bytes.
     * @param {number} i The index to read.
     * @return {number}
     */
    "read40Bit": function (bytes, i) {
        return readBytesAsBits(bytes, i, 5);
    },

    /**
     * Read 1 48-bit int from bytes.
     * @param {!Array<number>|Uint8Array} bytes An array of bytes.
     * @param {number} i The index to read.
     * @return {number}
     */
    "read48Bit": function (bytes, i) {
        return readBytesAsBits(bytes, i, 6);
    },

    /**
     * Read 1 64-bit double from bytes.
     * Thanks https://gist.github.com/kg/2192799
     * @param {!Array<number>|Uint8Array} bytes An array of bytes.
     * @param {number} x The index to read.
     * @return {number}
     */
    "read64BitFloat": function (bytes, x) {
        let binary = getBinary(bytes.slice(x, x + 8));
        let significandBin = "1" + binary.substr(1 + 11, 52);
        let val = 1;
        let significand = 0;
        let i = 0;
        while (i < significandBin.length) {
            significand += val * parseInt(significandBin.charAt(i), 10);
            val = val / 2;
            i++;
        }
        let sign = (binary.charAt(0) == "1") ? -1 : 1;
        let doubleValue = sign * significand *
            Math.pow(2, parseInt(binary.substr(1, 11), 2) - 1023);
        return doubleValue == -0 ? 0 : doubleValue;
    },

    /**
     * Read 1 char from bytes.
     * @param {!Array<number>|Uint8Array} bytes An array of bytes.
     * @param {number} i The index to read.
     * @return {string}
     */
    "readChar": function (bytes, i, type) {
        let chrs = "";
        let j = 0;
        let len = type.bits / 8;
        while(j < len) {
            chrs += String.fromCharCode(bytes[i+j]);
            j++;
        }
        return chrs;
    }
};

/**
 * Functions to write data to bytes.
 * @enum {Function}
 */
let BitWriter = {

    "write64BitFloat": function(bytes, number, j) {
        let bits = toFloat64(number);
        j = BitWriter["write32Bit"](bytes, bits[1], j);
        return BitWriter["write32Bit"](bytes, bits[0], j);
    },

    // Thanks https://github.com/majimboo/c-struct
    "write48Bit": function (bytes, number, j) {
        j = BitWriter["write40Bit"](bytes, number, j);
        bytes[j++] = number / 0x10000000000 & 0xFF;
        return j;
    },

    // Thanks https://github.com/majimboo/c-struct
    "write40Bit": function (bytes, number, j) {
        j = BitWriter["write32Bit"](bytes, number, j);
        bytes[j++] = number / 0x100000000 & 0xFF;
        return j;
    },

    "write32BitFloat": function (bytes, number, j) {
        f32[0] = number;
        j = BitWriter["write32Bit"](bytes, i32[0], j);
        return j;
    },

    "write32Bit": function (bytes, number, j) {
        j = BitWriter["write24Bit"](bytes, number, j);
        bytes[j++] = number >>> 24 & 0xFF;
        return j;
    },

    "write24Bit": function (bytes, number, j) {
        j = BitWriter["write16Bit"](bytes, number, j);
        bytes[j++] = number >>> 16 & 0xFF;
        return j;
    },

    "write16Bit": function (bytes, number, j) {
        bytes[j++] = number & 0xFF;
        bytes[j++] = number >>> 8 & 0xFF;
        return j;
    },

    "write16BitFloat": function (bytes, number, j) {
        let bits = toHalf(number);
        bytes[j] = bits & 0xFF;
        bytes[j+1] = bits >>> 8 & 0xFF;
        return j+2;
    },

    "write8Bit": function (bytes, number, j) {
        bytes[j++] = number & 0xFF;
        return j;
    },

    "write4Bit": function (bytes, number, j) {
        bytes[j++] = number & 0xF;
        return j;
    },

    "write2Bit": function (bytes, number, j) {
        bytes[j++] = number < 0 ? number + 4 : number;
        return j;
    },

    "write1Bit": function (bytes, number, j) {
        bytes[j++] = number ? 1 : 0;
        return j;
    },

    "writeString": function (bytes, string, j) {
        bytes[j++] = string.charCodeAt(0);
        return j;
    }
};

/**
 * Get a binary string representation of a value described as bytes.
 * @param {Array<number>|number} bytes The bytes.
 * @return {string}
 */
function getBinary(bytes) {
    let binary = "";
    let i = 0;
    let bytesLength = bytes.length;
    while(i < bytesLength) {
        let bits = bytes[i].toString(2);
        binary = Array(9 - bits.length).join("0") + bits + binary;
        i++;
    }
    return binary;
}

/**
 * Unpack a 64 bit float into two words.
 * Thanks https://stackoverflow.com/a/16043259
 * @param {number} value A float64 number.
 * @return {!Array<number>}
 */
function toFloat64(value) {
    if (value == 0) {
        return [0, 0];
    }
    let hiWord = 0;
    let loWord = 0;
    if (value <= 0) {
        hiWord = 0x80000000;
        value = -value;
    }
    let exponent = Math.floor(
        Math.log(value) / Math.log(2));
    let significand = Math.floor(
        (value / Math.pow(2, exponent)) * Math.pow(2, 52));
    loWord = significand & 0xFFFFFFFF;
    significand /= Math.pow(2, 32);
    exponent += 1023;
    hiWord = hiWord | (exponent << 20);
    hiWord = hiWord | (significand & ~(-1 << 20));
    return [hiWord, loWord];
}

/**
 * to-half: int bits of half-precision floating point values
 * Based on:
 * https://mail.mozilla.org/pipermail/es-discuss/2017-April/047994.html
 * https://github.com/rochars/byte-data
 * @param {number} val The float16 value.
 * @return {number}
 */
function toHalf(val) {
    f32[0] = val;
    let x = i32[0];
    let bits = (x >> 16) & 0x8000;
    let m = (x >> 12) & 0x07ff;
    let e = (x >> 23) & 0xff;
    if (e < 103) {
        return bits;
    }
    bits |= ((e - 112) << 10) | (m >> 1);
    bits += m & 1;
    return bits;
}

/**
 * Read a group of bytes by turning it to bits.
 * Useful for 40 & 48-bit, but underperform.
 * @param {!Array<number>|Uint8Array} bytes An array of bytes.
 * @param {number} i The index to read.
 * @param {number} numBytes The number of bytes
 *      (1 for 8-bit, 2 for 16-bit, etc).
 * @return {number}
 */
function readBytesAsBits(bytes, i, numBytes) {
    let j = numBytes-1;
    let byte = "";
    while (j >= 0) {
        let bits = bytes[j + i].toString(2);
        byte += Array(9 - bits.length).join("0") + bits;
        j--;
    }
    return parseInt(byte, 2);
}

module.exports.BitWriter = BitWriter;
module.exports.BitReader = BitReader;


1			/**
2			* bit-parser: Functions to read and write bytes.
3			* Copyright (c) 2017 Rafael da Silva Rocha.
4			* https://github.com/rochars/byte-data
5			* Float32 based on int-bits: https://github.com/Jam3/int-bits
6			*/
7
8			let f32 = new Float32Array(1);
9			let i32 = new Int32Array(f32.buffer);
10
11
12			/**
13			* Functions to read data from bytes.
14			* @enum {Function}
15			*/
16			const BitReader = {
17
18			/**
19			* Read 1 8-bit int from from bytes.
20			* @param {!Array<number>\|Uint8Array} bytes An array of bytes.
21			* @param {number} i The index to read.
22			* @return {number}
23			*/
24			"read8Bit": function (bytes, i) {
25			return bytes[i];
26			},
27
28			/**
29			* Read 1 16-bit int from from bytes.
30			* @param {!Array<number>\|Uint8Array} bytes An array of bytes.
31			* @param {number} i The index to read.
32			* @return {number}
33			*/
34			"read16Bit": function (bytes, i) {
35			return bytes[1 + i] << 8 \| bytes[i];
36			},
37
38			/**
39			* Read 1 16-bit float from from bytes.
40			* Thanks https://stackoverflow.com/a/8796597
41			* @param {!Array<number>\|Uint8Array} bytes An array of bytes.
42			* @param {number} i The index to read.
43			* @return {number}
44			*/
45			"read16BitFloat": function (bytes, i) {
46			let binary = parseInt(getBinary([bytes[i], bytes[i+1]]), 2);
47			let exponent = (binary & 0x7C00) >> 10;
48			let fraction = binary & 0x03FF;
49			let floatValue;
50			if (exponent) {
51			floatValue = Math.pow(2, exponent - 15) * (1 + fraction / 0x400);
52			} else {
53			floatValue = 6.103515625e-5 * (fraction / 0x400);
54			}
55			return floatValue * (binary >> 15 ? -1 : 1);
56			},
57
58			/**
59			* Read 1 24-bit int from from bytes.
60			* @param {!Array<number>\|Uint8Array} bytes An array of bytes.
61			* @param {number} i The index to read.
62			* @return {number}
63			*/
64			"read24Bit": function (bytes, i) {
65			return bytes[2 + i] << 16 \| BitReader["read16Bit"](bytes, i);
66			},
67
68			/**
69			* Read 1 32-bit int from from bytes.
70			* @param {!Array<number>\|Uint8Array} bytes An array of bytes.
71			* @param {number} i The index to read.
72			* @return {number}
73			*/
74			"read32Bit": function (bytes, i) {
75			return (bytes[3 + i] << 24 \|
76			BitReader["read24Bit"](bytes, i)) >>> 0;
77			},
78
79			/**
80			* Read 1 32-bit float from from bytes.
81			* @param {!Array<number>\|Uint8Array} bytes An array of bytes.
82			* @param {number} i The index to read.
83			* @return {number}
84			*/
85			"read32BitFloat": function (bytes, i) {
86			i32[0] = BitReader["read32Bit"](bytes, i);
87			return f32[0];
88			},
89
90			/**
91			* Read 1 40-bit int from from bytes.
92			* @param {!Array<number>\|Uint8Array} bytes An array of bytes.
93			* @param {number} i The index to read.
94			* @return {number}
95			*/
96			"read40Bit": function (bytes, i) {
97			return readBytesAsBits(bytes, i, 5);
98			},
99
100			/**
101			* Read 1 48-bit int from bytes.
102			* @param {!Array<number>\|Uint8Array} bytes An array of bytes.
103			* @param {number} i The index to read.
104			* @return {number}
105			*/
106			"read48Bit": function (bytes, i) {
107			return readBytesAsBits(bytes, i, 6);
108			},
109
110			/**
111			* Read 1 64-bit double from bytes.
112			* Thanks https://gist.github.com/kg/2192799
113			* @param {!Array<number>\|Uint8Array} bytes An array of bytes.
114			* @param {number} x The index to read.
115			* @return {number}
116			*/
117			"read64BitFloat": function (bytes, x) {
118			let binary = getBinary(bytes.slice(x, x + 8));
119			let significandBin = "1" + binary.substr(1 + 11, 52);
120			let val = 1;
121			let significand = 0;
122			let i = 0;
123			while (i < significandBin.length) {
124			significand += val * parseInt(significandBin.charAt(i), 10);
125			val = val / 2;
126			i++;
127			}
128			let sign = (binary.charAt(0) == "1") ? -1 : 1;
129			let doubleValue = sign * significand *
130			Math.pow(2, parseInt(binary.substr(1, 11), 2) - 1023);
131			return doubleValue == -0 ? 0 : doubleValue;
132			},
133
134			/**
135			* Read 1 char from bytes.
136			* @param {!Array<number>\|Uint8Array} bytes An array of bytes.
137			* @param {number} i The index to read.
138			* @return {string}
139			*/
140			"readChar": function (bytes, i, type) {
141			let chrs = "";
142			let j = 0;
143			let len = type.bits / 8;
144			while(j < len) {
145			chrs += String.fromCharCode(bytes[i+j]);
146			j++;
147			}
148			return chrs;
149			}
150			};
151
152			/**
153			* Functions to write data to bytes.
154			* @enum {Function}
155			*/
156			let BitWriter = {
157
158			"write64BitFloat": function(bytes, number, j) {
159			let bits = toFloat64(number);
160			j = BitWriter["write32Bit"](bytes, bits[1], j);
161			return BitWriter["write32Bit"](bytes, bits[0], j);
162			},
163
164			// Thanks https://github.com/majimboo/c-struct
165			"write48Bit": function (bytes, number, j) {
166			j = BitWriter["write40Bit"](bytes, number, j);
167			bytes[j++] = number / 0x10000000000 & 0xFF;
168			return j;
169			},
170
171			// Thanks https://github.com/majimboo/c-struct
172			"write40Bit": function (bytes, number, j) {
173			j = BitWriter["write32Bit"](bytes, number, j);
174			bytes[j++] = number / 0x100000000 & 0xFF;
175			return j;
176			},
177
178			"write32BitFloat": function (bytes, number, j) {
179			f32[0] = number;
180			j = BitWriter["write32Bit"](bytes, i32[0], j);
181			return j;
182			},
183
184			"write32Bit": function (bytes, number, j) {
185			j = BitWriter["write24Bit"](bytes, number, j);
186			bytes[j++] = number >>> 24 & 0xFF;
187			return j;
188			},
189
190			"write24Bit": function (bytes, number, j) {
191			j = BitWriter["write16Bit"](bytes, number, j);
192			bytes[j++] = number >>> 16 & 0xFF;
193			return j;
194			},
195
196			"write16Bit": function (bytes, number, j) {
197			bytes[j++] = number & 0xFF;
198			bytes[j++] = number >>> 8 & 0xFF;
199			return j;
200			},
201
202			"write16BitFloat": function (bytes, number, j) {
203			let bits = toHalf(number);
204			bytes[j] = bits & 0xFF;
205			bytes[j+1] = bits >>> 8 & 0xFF;
206			return j+2;
207			},
208
209			"write8Bit": function (bytes, number, j) {
210			bytes[j++] = number & 0xFF;
211			return j;
212			},
213
214			"write4Bit": function (bytes, number, j) {
215			bytes[j++] = number & 0xF;
216			return j;
217			},
218
219			"write2Bit": function (bytes, number, j) {
220			bytes[j++] = number < 0 ? number + 4 : number;
221			return j;
222			},
223
224			"write1Bit": function (bytes, number, j) {
225			bytes[j++] = number ? 1 : 0;
226			return j;
227			},
228
229			"writeString": function (bytes, string, j) {
230			bytes[j++] = string.charCodeAt(0);
231			return j;
232			}
233			};
234
235			/**
236			* Get a binary string representation of a value described as bytes.
237			* @param {Array<number>\|number} bytes The bytes.
238			* @return {string}
239			*/
240			function getBinary(bytes) {
241			let binary = "";
242			let i = 0;
243			let bytesLength = bytes.length;
244			while(i < bytesLength) {
245			let bits = bytes[i].toString(2);
246			binary = Array(9 - bits.length).join("0") + bits + binary;
247			i++;
248			}
249			return binary;
250			}
251
252			/**
253			* Unpack a 64 bit float into two words.
254			* Thanks https://stackoverflow.com/a/16043259
255			* @param {number} value A float64 number.
256			* @return {!Array<number>}
257			*/
258			function toFloat64(value) {
259			if (value == 0) {
260			return [0, 0];
261			}
262			let hiWord = 0;
263			let loWord = 0;
264			if (value <= 0) {
265			hiWord = 0x80000000;
266			value = -value;
267			}
268			let exponent = Math.floor(
269			Math.log(value) / Math.log(2));
270			let significand = Math.floor(
271			(value / Math.pow(2, exponent)) * Math.pow(2, 52));
272			loWord = significand & 0xFFFFFFFF;
273			significand /= Math.pow(2, 32);
274			exponent += 1023;
275			hiWord = hiWord \| (exponent << 20);
276			hiWord = hiWord \| (significand & ~(-1 << 20));
277			return [hiWord, loWord];
278			}
279
280			/**
281			* to-half: int bits of half-precision floating point values
282			* Based on:
283			* https://mail.mozilla.org/pipermail/es-discuss/2017-April/047994.html
284			* https://github.com/rochars/byte-data
285			* @param {number} val The float16 value.
286			* @return {number}
287			*/
288			function toHalf(val) {
289			f32[0] = val;
290			let x = i32[0];
291			let bits = (x >> 16) & 0x8000;
292			let m = (x >> 12) & 0x07ff;
293			let e = (x >> 23) & 0xff;
294			if (e < 103) {
295			return bits;
296			}
297			bits \|= ((e - 112) << 10) \| (m >> 1);
298			bits += m & 1;
299			return bits;
300			}
301
302			/**
303			* Read a group of bytes by turning it to bits.
304			* Useful for 40 & 48-bit, but underperform.
305			* @param {!Array<number>\|Uint8Array} bytes An array of bytes.
306			* @param {number} i The index to read.
307			* @param {number} numBytes The number of bytes
308			* (1 for 8-bit, 2 for 16-bit, etc).
309			* @return {number}
310			*/
311			function readBytesAsBits(bytes, i, numBytes) {
312			let j = numBytes-1;
313			let byte = "";
314			while (j >= 0) {
315			let bits = bytes[j + i].toString(2);
316			byte += Array(9 - bits.length).join("0") + bits;
317			j--;
318			}
319			return parseInt(byte, 2);
320			}
321
322			module.exports.BitWriter = BitWriter;
323			module.exports.BitReader = BitReader;
324

rochars / byte-data

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bit-parser.js ➔ readBytesAsBits A

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