44 lines
1.2 KiB
JavaScript
44 lines
1.2 KiB
JavaScript
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function decodeFloat32(bytes) {
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var sign = (bytes & 0x80000000) ? -1 : 1;
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var exponent = ((bytes >> 23) & 0xFF) - 127;
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var significand = (bytes & ~(-1 << 23));
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if (exponent == 128)
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return sign * ((significand) ? Number.NaN : Number.POSITIVE_INFINITY);
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if (exponent == -127) {
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if (significand == 0) return sign * 0.0;
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exponent = -126;
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significand /= (1 << 22);
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} else significand = (significand | (1 << 23)) / (1 << 23);
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return sign * significand * Math.pow(2, exponent);
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}
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function decodeInt16(bytes) {
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if ((bytes & 1 << 15) > 0) { // value is negative (16bit 2's complement)
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bytes = ((~bytes) & 0xffff) + 1; // invert 16bits & add 1 => now positive value
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bytes = bytes * -1;
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}
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return bytes;
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}
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function int16_LE(bytes, idx) {
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bytes = bytes.slice(idx || 0);
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return bytes[0] << 0 | bytes[1] << 8;
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}
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function int32_LE(bytes, idx) {
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bytes = bytes.slice(idx || 0);
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return bytes[0] << 0 | bytes[1] << 8 | bytes[2] << 16 | bytes[3] << 24;
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}
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function Decoder(bytes, port) {
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// Decode an uplink message from a buffer
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// (array) of bytes to an object of fields.
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var decoded = {
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co2: decodeFloat32(int32_LE(bytes, 0)),
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};
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return decoded;
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}
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