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#1 Nov. 9, 2005 00:26:31

Peter J.
Registered: 2009-11-02
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[Mspgcc-users] msp430-libc rand function


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
#endifSo you get a different RAND_MAX depending on the order which you includefiles?The linux man page for int rand() says that rand() generates a randomnumber from 0 to RAND_MAX, the msp430-libc implementation generates aint rand from -32768 to 32767.I don't want to get into arguments about the randomness of rand(), itdoes what I want just fine, although there are a few problems with theimplementation, that I think need fixing.Attached is a diff file against the msp430-libc to fix both of theseproblems. Could someone put this into the CVS.--
Peter Jansen

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Visit our web site athttp://www.aad.gov.au/___________________________________________________________________________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;

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