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Greatly reduced error rate of WMath map() roundtrip #309

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Greatly reduced error rate of WMath map() roundtrip #309

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c265ddb
Greatly reduces error rate (half, or 0 zero errors, depends on in/out…
dok-net Jan 21, 2020
b02d22a
Clarify input constraints via comment.
dok-net Feb 6, 2021
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8 changes: 7 additions & 1 deletion cores/arduino/WMath.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -49,9 +49,15 @@ long random(long howsmall, long howbig)
return random(diff) + howsmall;
}

// well-defined for in_min < in_max, in_min <= x <= in_max,
// out_min <= out_max
long map(long x, long in_min, long in_max, long out_min, long out_max)
{
return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
const long dividend = out_max - out_min;
const long divisor = in_max - in_min;
const long delta = x - in_min;

return (delta * dividend + (divisor / 2)) / divisor + out_min;
}

unsigned int makeWord(unsigned int w) { return w; }
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