Created
September 11, 2018 02:12
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Encoding float value as per google protobuf implementation
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| const assert = require('assert'); | |
| //var buf = new Uint8Array(4); | |
| var buf = []; | |
| var split64High, split64Low; | |
| BinaryConstants = { | |
| FLOAT32_MIN : 1.1754943508222875e-38, | |
| FLOAT32_MAX : 3.4028234663852886e+38, | |
| TWO_TO_23 : 8388608 | |
| } | |
| var splitFloat32 = function(value) { | |
| var sign = (value < 0) ? 1 : 0; | |
| value = sign ? -value : value; | |
| var exp; | |
| var mant; | |
| // Handle zeros. | |
| if (value === 0) { | |
| if ((1 / value) > 0) { | |
| // Positive zero. | |
| split64High = 0; | |
| split64Low = 0x00000000; | |
| } else { | |
| // Negative zero. | |
| split64High = 0; | |
| split64Low = 0x80000000; | |
| } | |
| return; | |
| } | |
| // Handle nans. | |
| if (isNaN(value)) { | |
| split64High = 0; | |
| split64Low = 0x7FFFFFFF; | |
| return; | |
| } | |
| // Handle infinities. | |
| if (value > BinaryConstants.FLOAT32_MAX) { | |
| split64High = 0; | |
| split64Low = ((sign << 31) | (0x7F800000)) >>> 0; | |
| return; | |
| } | |
| // Handle denormals. | |
| if (value < BinaryConstants.FLOAT32_MIN) { | |
| // Number is a denormal. | |
| mant = Math.round(value / Math.pow(2, -149)); | |
| split64High = 0; | |
| split64Low = ((sign << 31) | mant) >>> 0; | |
| return; | |
| } | |
| exp = Math.floor(Math.log(value) / Math.LN2); | |
| mant = value * Math.pow(2, -exp); | |
| mant = Math.round(mant * BinaryConstants.TWO_TO_23) & 0x7FFFFF; | |
| split64High = 0; | |
| split64Low = ((sign << 31) | ((exp + 127) << 23) | mant) >>> 0; | |
| }; | |
| var writeUint32 = function(value) { | |
| console.log(value) | |
| assert(value == Math.floor(value)); | |
| assert((value >= 0) && (value < BinaryConstants.TWO_TO_32)); | |
| buf.push((value >>> 0) & 0xFF); | |
| buf.push((value >>> 8) & 0xFF); | |
| buf.push((value >>> 16) & 0xFF); | |
| buf.push((value >>> 24) & 0xFF); | |
| }; | |
| var writeFloat = function(value) { | |
| assert((value >= -BinaryConstants.FLOAT32_MAX) && | |
| (value <= BinaryConstants.FLOAT32_MAX)); | |
| splitFloat32(value); | |
| writeUint32(split64Low); | |
| }; | |
| //writeFloat(987654321); | |
| //writeFloat(987654336); | |
| writeFloat(34028); | |
| console.log(buf); |
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