rffti1.c

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/* rffti1.f -- translated by f2c (version 20100827).
   You must link the resulting object file with libf2c:
    on Microsoft Windows system, link with libf2c.lib;
    on Linux or Unix systems, link with .../path/to/libf2c.a -lm
    or, if you install libf2c.a in a standard place, with -lf2c -lm
    -- in that order, at the end of the command line, as in
        cc *.o -lf2c -lm
    Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,
 
        http://www.netlib.org/f2c/libf2c.zip
*/
 
#include "f2c.h"
 
/*     * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/*     *                                                               * */
/*     *                  copyright (c) 2011 by UCAR                   * */
/*     *                                                               * */
/*     *       University Corporation for Atmospheric Research         * */
/*     *                                                               * */
/*     *                      all rights reserved                      * */
/*     *                                                               * */
/*     *                     FFTPACK  version 5.1                      * */
/*     *                                                               * */
/*     *                 A Fortran Package of Fast Fourier             * */
/*     *                                                               * */
/*     *                Subroutines and Example Programs               * */
/*     *                                                               * */
/*     *                             by                                * */
/*     *                                                               * */
/*     *               Paul Swarztrauber and Dick Valent               * */
/*     *                                                               * */
/*     *                             of                                * */
/*     *                                                               * */
/*     *         the National Center for Atmospheric Research          * */
/*     *                                                               * */
/*     *                Boulder, Colorado  (80307)  U.S.A.             * */
/*     *                                                               * */
/*     *                   which is sponsored by                       * */
/*     *                                                               * */
/*     *              the National Science Foundation                  * */
/*     *                                                               * */
/*     * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
 
/* Subroutine */ int rffti1_(integer *n, doublereal *wa, doublereal *fac)
{
    /* Initialized data */
 
    static integer ntryh[4] = { 4,2,3,5 };
 
    /* System generated locals */
    integer i__1, i__2, i__3;
 
    /* Builtin functions */
    double atan(doublereal), cos(doublereal), sin(doublereal);
 
    /* Local variables */
    integer i__, j, k1, l1, l2, ib;
    doublereal fi;
    integer ld, ii, nf, ip, nl, is, nq, nr;
    doublereal arg;
    integer ido, ipm;
    doublereal tpi;
    integer nfm1;
    doublereal argh;
    integer ntry;
    doublereal argld;
 
    /* Parameter adjustments */
    --wa;
    --fac;
 
    /* Function Body */
 
    nl = *n;
    nf = 0;
    j = 0;
L101:
    ++j;
    if (j - 4 <= 0) {
    goto L102;
    } else {
    goto L103;
    }
L102:
    ntry = ntryh[j - 1];
    goto L104;
L103:
    ntry += 2;
L104:
    nq = nl / ntry;
    nr = nl - ntry * nq;
    if (nr != 0) {
    goto L101;
    } else {
    goto L105;
    }
L105:
    ++nf;
    fac[nf + 2] = (doublereal) ntry;
    nl = nq;
    if (ntry != 2) {
    goto L107;
    }
    if (nf == 1) {
    goto L107;
    }
    i__1 = nf;
    for (i__ = 2; i__ <= i__1; ++i__) {
    ib = nf - i__ + 2;
    fac[ib + 2] = fac[ib + 1];
/* L106: */
    }
    fac[3] = 2.;
L107:
    if (nl != 1) {
    goto L104;
    }
    fac[1] = (doublereal) (*n);
    fac[2] = (doublereal) nf;
    tpi = atan(1.) * 8.;
    argh = tpi / (doublereal) (*n);
    is = 0;
    nfm1 = nf - 1;
    l1 = 1;
    if (nfm1 == 0) {
    return 0;
    }
    i__1 = nfm1;
    for (k1 = 1; k1 <= i__1; ++k1) {
    ip = (integer) fac[k1 + 2];
    ld = 0;
    l2 = l1 * ip;
    ido = *n / l2;
    ipm = ip - 1;
    i__2 = ipm;
    for (j = 1; j <= i__2; ++j) {
        ld += l1;
        i__ = is;
        argld = (doublereal) ld * argh;
        fi = 0.;
        i__3 = ido;
        for (ii = 3; ii <= i__3; ii += 2) {
        i__ += 2;
        fi += 1.;
        arg = fi * argld;
        wa[i__ - 1] = cos(arg);
        wa[i__] = sin(arg);
/* L108: */
        }
        is += ido;
/* L109: */
    }
    l1 = l2;
/* L110: */
    }
    return 0;
} /* rffti1_ */