/*  sincosf.c: Computes sin or cos of a 32-bit float as outlined in [1]

    Copyright (C) 2001, 2002  Jesus Calvino-Fraga, jesusc@ieee.org

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA */

/* [1] William James Cody and W.  M.  Waite.  _Software manual for the
   elementary functions_, Englewood Cliffs, N.J.:Prentice-Hall, 1980. */

/* Version 1.0 - Initial release */

#include <math.h>
#include <errno.h>
#include <stdbool.h>

#define r1      -0.1666665668E+0
#define r2       0.8333025139E-2
#define r3      -0.1980741872E-3
#define r4       0.2601903036E-5

/* PI=C1+C2 */
#define C1       3.140625
#define C2       9.676535897E-4

/*A reasonable value for YMAX is the int part of PI*B**(t/2)=3.1416*2**(12)*/
#define YMAX     12867.0

float sincosf(const float x, const int iscos)
{
    float y, f, r, g, XN;
    int N;
        BOOL sign;

    if(iscos)
    {
        y=fabsf(x)+HALF_PI;
        sign=0;
    }
    else
    {
        if(x<0.0)
            { y=-x; sign=1; }
        else
            { y=x; sign=0; }
    }

    if(y>YMAX)
    {
        errno=ERANGE;
        return 0.0;
    }

    /*Round y/PI to the nearest integer*/
    N=((y*iPI)+0.5); /*y is positive*/

    /*If N is odd change sign*/
    if(N&1) sign=!sign;

    XN=N;
    /*Cosine required? (is done here to keep accuracy)*/
    if(iscos) XN-=0.5;

    y=fabsf(x);
    r=(int)y;
    g=y-r;
    f=((r-XN*C1)+g)-XN*C2;

    g=f*f;
    if(g>EPS2) //Used to be if(fabsf(f)>EPS)
    {
        r=(((r4*g+r3)*g+r2)*g+r1)*g;
        f+=f*r;
    }
    return (sign?-f:f);
}

Youve got to deside if you have enough time to run that for each sine or cosine or a lookup table would be better.Obviously only you can deside if you really need to use floating point but most applications very rarely do.