/* @SUBTITLE "alloc2d - matrix memory allocation" */
#include <stdio.h>

/* Builds a C-like 2D matrix, with a side-vector for pointer-indirect
 * access to the matrix. 
 */

extern char *alloc();		/* used for memory allocation */

char **					/* pointer to matrix */
alloc2d(rows, cols, elsize)
	int rows, cols;		/* number of rows and cols */
	int elsize;			/* size of each matrix element (bytes) */
{
    char *block;			/* the big block that is the matrix */
    char **side;			/* the side vector pointing to rows */
    int rowsize = cols * elsize; /* length of each row */
    char *arow;			/* pointer to a row */
    int row;				/* index of a row */

    block = alloc(rows * cols * elsize);
    side = (char **) alloc(rows * sizeof(char *));

    arow = block;
    for (row = 0; row < rows; row++) {
	   side[row] = arow;
	   arow += rowsize;
    }

    return(side);
}