60 lines
1.2 KiB
JavaScript
60 lines
1.2 KiB
JavaScript
const { Errors } = require('./enig_error');
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//
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// Utils for dealing with Microsoft Binary Format (MBF) used
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// in various BASIC languages, etc.
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//
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// - https://en.wikipedia.org/wiki/Microsoft_Binary_Format
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// - https://stackoverflow.com/questions/2268191/how-to-convert-from-ieee-python-float-to-microsoft-basic-float
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//
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// Number to 32bit MBF
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const numToMbf32 = v => {
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const mbf = Buffer.alloc(4);
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if (0 === v) {
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return mbf;
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}
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const ieee = Buffer.alloc(4);
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ieee.writeFloatLE(v, 0);
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const sign = ieee[3] & 0x80;
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let exp = (ieee[3] << 1) | (ieee[2] >> 7);
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if (exp === 0xfe) {
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throw Errors.Invalid(`${v} cannot be converted to mbf`);
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}
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exp += 2;
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mbf[3] = exp;
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mbf[2] = sign | (ieee[2] & 0x7f);
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mbf[1] = ieee[1];
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mbf[0] = ieee[0];
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return mbf;
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};
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const mbf32ToNum = mbf => {
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if (0 === mbf[3]) {
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return 0.0;
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}
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const ieee = Buffer.alloc(4);
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const sign = mbf[2] & 0x80;
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const exp = mbf[3] - 2;
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ieee[3] = sign | (exp >> 1);
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ieee[2] = (exp << 7) | (mbf[2] & 0x7f);
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ieee[1] = mbf[1];
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ieee[0] = mbf[0];
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return ieee.readFloatLE(0);
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};
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module.exports = {
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numToMbf32,
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mbf32ToNum,
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};
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