random.c

来自「用于TM1300/PNX1300系列DSP（主要用于视频处理）的各种滤波器源码」· C语言 代码 · 共 35 行

/************************************************************************/
/*	C source file:	ran_gen.c					*/
/*	Author:		Jean Gobert LEP ([e-mail])		*/
/*	Creation date:	14 Oct 1996					*/
/*	Last modified:							*/
/*	abstract: 	this module generates random pixels.		*/
/*									*/
/*	ran_gen [<low> [<high> [<number of blocks>]]]	 		*/
/*	defauls : 0      255        10000				*/
/*	output on stdout						*/
/************************************************************************/
#include "tc.h"


/*	random number generator specified in the appendix to	*/
/*	Specification for p*64 kbit/s				*/

/* L and H must be longs, i.e., 32 bits */
long	rand_dct(		/* returned random number */
		long	L,	/* low bound of range */
		long	H)	/* high bound of range */
{
	static	double	z	= (double)0x7fffffff;

	long	i, j;
	double	x;	/* double is 64 bits */

	state->randx	= (state->randx * 1103515245) + 12345;
	i	= state->randx & 0x7ffffffe;	/* keep 30 bits */
	x	= ((double)i) / z;	/* range 0 to 0.99999... */
	x	*= (L + H + 1);		/* range 0 to < L + H + 1 */
	j	= x;			/* truncate to integer */
	return	(j - L);		/* range -L to H */
}