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Unbiased random (#2468)

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* An example to read high frequency analog data using i2s_adc

* Changed random() to use Lemire's method for bounding
This commit is contained in:
lbernstone 2019-02-18 03:18:49 -07:00 committed by Me No Dev
parent 89d6b895d1
commit 2bb32bd4b0
1 changed files with 16 additions and 3 deletions
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19
cores/esp32/WMath.cpp
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@ -37,10 +37,23 @@ void randomSeed(unsigned long seed)
long random(long howbig) long random(long howbig)
{ {
if(howbig == 0) { uint32_t x = esp_random();
return 0; uint64_t m = uint64_t(x) * uint64_t(howbig);
uint32_t l = uint32_t(m);
if (l < howbig) {
uint32_t t = -howbig;
if (t >= howbig) {
t -= howbig;
if (t >= howbig)
t %= howbig;
}
while (l < t) {
x = esp_random();
m = uint64_t(x) * uint64_t(howbig);
l = uint32_t(m);
}
} }
return esp_random() % howbig; return m >> 32;
} }
long random(long howsmall, long howbig) long random(long howsmall, long howbig)