Hi All,
I have some issues with the rand function in msp430-libc,
include/stdio.h says,
#ifndef RAND_MAX
#define RAND_MAX 0x7fffffffL
#endif
include/limits.h says,
#define INT_MAX 32767 /* maximum (signed) int value */
...
#ifndef RAND_MAX
#define RAND_MAX INT_MAX
#endif
So you get a different RAND_MAX depending on the order which you include
files?
The linux man page for int rand() says that rand() generates a random
number from 0 to RAND_MAX, the msp430-libc implementation generates a
int rand from -32768 to 32767.
I don't want to get into arguments about the randomness of rand(), it
does what I want just fine, although there are a few problems with the
implementation, that I think need fixing.
Attached is a diff file against the msp430-libc to fix both of these
problems. Could someone put this into the CVS.
--
Peter Jansen
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Index: include/stdlib.h
===================================================================
RCS file: /cvsroot/mspgcc/msp430-libc/include/stdlib.h,v
retrieving revision 1.11
diff -r1.11 stdlib.h
107c107
< #define RAND_MAX 0x7fffffffL
---
> #define RAND_MAX 0x7fffL
Index: src/stdlib/rand.c
===================================================================
RCS file: /cvsroot/mspgcc/msp430-libc/src/stdlib/rand.c,v
retrieving revision 1.2
diff -r1.2 rand.c
52c52,63
< return ((*ctx = *ctx * 1103515245 + 12345) % ((unsigned long int)RAND_MAX
+ 1));
---
> long hi, lo, x;
>
> hi = *ctx / 127773L;
> lo = *ctx % 127773L;
> x = 16807L * lo - 2836L * hi;
> if (x <= 0)
> x += 0x7fffffffL;
>
> *ctx = (unsigned long)x;
> x = x % ((unsigned long)RAND_MAX_X +1);
>
> return x;
