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Non-uniform random floats (_randommodule.c) #31606

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Non-uniform random floats (_randommodule.c) #31606

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Non-uniform random floats (_randommodule.c) 
The original implementation produces an output that has some bias in the lower bits of mantissa (more 0's than 1's). That's because we try to fit 2^53 pigeons into 2^52 available holes, so rounding to even is unavoidable. My solution is to generate just 2^52 pigeons using the expression (randbits_53 | 1) to generate 2^52 odd numbers only in the range [1, 2^53-1] , with zero cannot be generated. but, the distribution of mantissa bits becomes more uniform.
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@amrali-eg
amrali-eg authored Feb 27, 2022
commit 82684a205c2849525ced5f463615f5e8acbcc6a2
2 changes: 1 addition & 1 deletion Modules/_randommodule.c
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Expand Up @@ -177,7 +177,7 @@ _random_Random_random_impl(RandomObject *self)
/*[clinic end generated code: output=117ff99ee53d755c input=afb2a59cbbb00349]*/
{
uint32_t a=genrand_uint32(self)>>5, b=genrand_uint32(self)>>6;
return PyFloat_FromDouble((a*67108864.0+b)*(1.0/9007199254740992.0));
return PyFloat_FromDouble(((((uint64_t)(a)<<26)|b)|1)*(1.0/9007199254740992.0));
}

/* initializes mt[N] with a seed */
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