#include "cblas.h"
#include "f2cP.h"

/* Subroutine */ int dspr_(const char *uplo, integer *n, double *alpha, 
	double *x, integer *incx, double *ap)
{
    /* System generated locals */
    integer i__1, i__2;

    /* Local variables */
    integer i__, j, k, kk, ix, jx, kx, info;
    double temp;
 
 

/*     .. Scalar Arguments .. */
/*     .. */
/*     .. Array Arguments .. */
/*     .. */

/*  Purpose */
/*  ======= */

/*  DSPR    performs the symmetric rank 1 operation */

/*     A := alpha*x*x' + A, */

/*  where alpha is a real scalar, x is an n element vector and A is an */
/*  n by n symmetric matrix, supplied in packed form. */

/*  Arguments */
/*  ========== */

/*  UPLO   - CHARACTER*1. */
/*           On entry, UPLO specifies whether the upper or lower */
/*           triangular part of the matrix A is supplied in the packed */
/*           array AP as follows: */

/*              UPLO = 'U' or 'u'   The upper triangular part of A is */
/*                                  supplied in AP. */

/*              UPLO = 'L' or 'l'   The lower triangular part of A is */
/*                                  supplied in AP. */

/*           Unchanged on exit. */

/*  N      - INTEGER. */
/*           On entry, N specifies the order of the matrix A. */
/*           N must be at least zero. */
/*           Unchanged on exit. */

/*  ALPHA  - DOUBLE PRECISION. */
/*           On entry, ALPHA specifies the scalar alpha. */
/*           Unchanged on exit. */

/*  X      - DOUBLE PRECISION array of dimension at least */
/*           ( 1 + ( n - 1 )*abs( INCX ) ). */
/*           Before entry, the incremented array X must contain the n */
/*           element vector x. */
/*           Unchanged on exit. */

/*  INCX   - INTEGER. */
/*           On entry, INCX specifies the increment for the elements of */
/*           X. INCX must not be zero. */
/*           Unchanged on exit. */

/*  AP     - DOUBLE PRECISION array of DIMENSION at least */
/*           ( ( n*( n + 1 ) )/2 ). */
/*           Before entry with  UPLO = 'U' or 'u', the array AP must */
/*           contain the upper triangular part of the symmetric matrix */
/*           packed sequentially, column by column, so that AP( 1 ) */
/*           contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 1, 2 ) */
/*           and a( 2, 2 ) respectively, and so on. On exit, the array */
/*           AP is overwritten by the upper triangular part of the */
/*           updated matrix. */
/*           Before entry with UPLO = 'L' or 'l', the array AP must */
/*           contain the lower triangular part of the symmetric matrix */
/*           packed sequentially, column by column, so that AP( 1 ) */
/*           contains a( 1, 1 ), AP( 2 ) and AP( 3 ) contain a( 2, 1 ) */
/*           and a( 3, 1 ) respectively, and so on. On exit, the array */
/*           AP is overwritten by the lower triangular part of the */
/*           updated matrix. */


/*  Level 2 Blas routine. */

/*  -- Written on 22-October-1986. */
/*     Jack Dongarra, Argonne National Lab. */
/*     Jeremy Du Croz, Nag Central Office. */
/*     Sven Hammarling, Nag Central Office. */
/*     Richard Hanson, Sandia National Labs. */


/*     .. Parameters .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. External Functions .. */
/*     .. */
/*     .. External Subroutines .. */
/*     .. */

/*     Test the input parameters. */

    /* Parameter adjustments */
    --ap;
    --x;

    /* Function Body */
    info = 0;
    if (! lsame_(uplo, "U") && ! lsame_(uplo, "L")) {
	info = 1;
    } else if (*n < 0) {
	info = 2;
    } else if (*incx == 0) {
	info = 5;
    }
    if (info != 0) {
	xerbla_("DSPR  ", &info);
	return 0;
    }

/*     Quick return if possible. */

    if (*n == 0 || *alpha == 0.) {
	return 0;
    }

/*     Set the start point in X if the increment is not unity. */

    if (*incx <= 0) {
	kx = 1 - (*n - 1) * *incx;
    } else if (*incx != 1) {
	kx = 1;
    }

/*     Start the operations. In this version the elements of the array AP */
/*     are accessed sequentially with one pass through AP. */

    kk = 1;
    if (lsame_(uplo, "U")) {

/*        Form  A  when upper triangle is stored in AP. */

	if (*incx == 1) {
	    i__1 = *n;
	    for (j = 1; j <= i__1; ++j) {
		if (x[j] != 0.) {
		    temp = *alpha * x[j];
		    k = kk;
		    i__2 = j;
		    for (i__ = 1; i__ <= i__2; ++i__) {
			ap[k] += x[i__] * temp;
			++k;
/* L10: */
		    }
		}
		kk += j;
/* L20: */
	    }
	} else {
	    jx = kx;
	    i__1 = *n;
	    for (j = 1; j <= i__1; ++j) {
		if (x[jx] != 0.) {
		    temp = *alpha * x[jx];
		    ix = kx;
		    i__2 = kk + j - 1;
		    for (k = kk; k <= i__2; ++k) {
			ap[k] += x[ix] * temp;
			ix += *incx;
/* L30: */
		    }
		}
		jx += *incx;
		kk += j;
/* L40: */
	    }
	}
    } else {

/*        Form  A  when lower triangle is stored in AP. */

	if (*incx == 1) {
	    i__1 = *n;
	    for (j = 1; j <= i__1; ++j) {
		if (x[j] != 0.) {
		    temp = *alpha * x[j];
		    k = kk;
		    i__2 = *n;
		    for (i__ = j; i__ <= i__2; ++i__) {
			ap[k] += x[i__] * temp;
			++k;
/* L50: */
		    }
		}
		kk = kk + *n - j + 1;
/* L60: */
	    }
	} else {
	    jx = kx;
	    i__1 = *n;
	    for (j = 1; j <= i__1; ++j) {
		if (x[jx] != 0.) {
		    temp = *alpha * x[jx];
		    ix = jx;
		    i__2 = kk + *n - j;
		    for (k = kk; k <= i__2; ++k) {
			ap[k] += x[ix] * temp;
			ix += *incx;
/* L70: */
		    }
		}
		jx += *incx;
		kk = kk + *n - j + 1;
/* L80: */
	    }
	}
    }

    return 0;

/*     End of DSPR  . */

} /* dspr_ */
