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Refactor times inverse of sqrt 2 calculation #21293

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merged 2 commits into from
Jul 7, 2023
Merged

Refactor times inverse of sqrt 2 calculation #21293

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2a81d5d
Refactor times inverse of sqrt 2 calculation
filterpaper Jun 5, 2023
dc347f8
Use constant unsigned type for denominator
filterpaper Jun 19, 2023
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15 changes: 10 additions & 5 deletions quantum/mousekey.c
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Original file line number Diff line number Diff line change
Expand Up @@ -25,11 +25,16 @@
#include "mousekey.h"

static inline int8_t times_inv_sqrt2(int8_t x) {
// 181/256 is pretty close to 1/sqrt(2)
// 0.70703125 0.707106781
// 1 too small for x=99 and x=198
// This ends up being a mult and discard lower 8 bits
return (x * 181) >> 8;
// 181/256 (0.70703125) is used as an approximation for 1/sqrt(2)
// because it is close to the exact value which is 0.707106781
const int16_t n = x * 181;
const uint16_t d = 256;

// To ensure that the integer result is rounded accurately after
// division, check the sign of the numerator:
// If negative, subtract half of the denominator before dividing
// Otherwise, add half of the denominator before dividing
return n < 0 ? (n - d / 2) / d : (n + d / 2) / d;
}

static report_mouse_t mouse_report = {0};
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