8protons 8protons - 15 days ago 5
C Question

Cant solve "warning: conversion to 'long unsigned int' from 'int'"

When I compile mt19937ar.c, a pretty standard random number generator, I keep getting issues with a bit of code that I need from it.


In function 'init_genrand':

warning: conversion to 'long unsigned int' from 'int' may change the sign of the result


/* Period parameters */
#define N 624
#define M 397
#define MATRIX_A 0x9908b0dfUL /* constant vector a */
#define UPPER_MASK 0x80000000UL /* most significant w-r bits */
#define LOWER_MASK 0x7fffffffUL /* least significant r bits */

static unsigned long mt[N]; /* the array for the state vector */
static int mti=N+1; /* mti==N+1 means mt[N] is not initialized */

/* initializes mt[N] with a seed */
void init_genrand(unsigned long s)
{
mt[0]= s & 0xffffffffUL;
for (mti=1; mti<N; mti++) {
mt[mti] =
(1812433253UL * (mt[mti-1] ^ (mt[mti-1] >> 30)) + mti);
/* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
/* In the previous versions, MSBs of the seed affect */
/* only MSBs of the array mt[]. */
/* 2002/01/09 modified by Makoto Matsumoto */
mt[mti] &= 0xffffffffUL;
/* for >32 bit machines */
}
}


Specifically, the error is with

mt[mti] =
(1812433253UL * (mt[mti-1] ^ (mt[mti-1] >> 30)) + mti);


I've tried casting it via

mt[mti] = (long unsigned int)
(1812433253UL * (mt[mti-1] ^ (mt[mti-1] >> 30)) + mti);


which really doesn't make sense to do but I'm just attempting something. This code is from 1997- figured someone would have caught this by now and fixed it. How can I solve this? Or get my compiler to stop crying about it?

Answer

You need to change type of mti to unsigned int or unsigned long int

static unsigned int mti = N+1;

Because mti will be promoted to unsigned long in your given expression