/* k_rem_pio2f.c -- float version of k_rem_pio2.c
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 */

/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

#if defined(LIBM_SCCS) && !defined(lint)
static char rcsid[] = "$NetBSD: k_rem_pio2f.c,v 1.4 1995/05/10 20:46:28 jtc Exp $";
#endif

#include <math.h>
#include <math-narrow-eval.h>
#include <math_private.h>
#include <libc-diag.h>

/* In the float version, the input parameter x contains 8 bit
   integers, not 24 bit integers.  113 bit precision is not supported.  */

static const int init_jk[] = {4,7,9}; /* initial value for jk */

static const float PIo2[] = {
  1.5703125000e+00, /* 0x3fc90000 */
  4.5776367188e-04, /* 0x39f00000 */
  2.5987625122e-05, /* 0x37da0000 */
  7.5437128544e-08, /* 0x33a20000 */
  6.0026650317e-11, /* 0x2e840000 */
  7.3896444519e-13, /* 0x2b500000 */
  5.3845816694e-15, /* 0x27c20000 */
  5.6378512969e-18, /* 0x22d00000 */
  8.3009228831e-20, /* 0x1fc40000 */
  3.2756352257e-22, /* 0x1bc60000 */
  6.3331015649e-25, /* 0x17440000 */
};

static const float
zero   = 0.0,
one    = 1.0,
two8   =  2.5600000000e+02, /* 0x43800000 */
twon8  =  3.9062500000e-03; /* 0x3b800000 */

int __kernel_rem_pio2f(float *x, float *y, int e0, int nx, int prec, const int32_t *ipio2)
{
	int32_t jz,jx,jv,jp,jk,carry,n,iq[20],i,j,k,m,q0,ih;
	float z,fw,f[20],fq[20],q[20];

    /* initialize jk*/
	jk = init_jk[prec];
	jp = jk;

    /* determine jx,jv,q0, note that 3>q0 */
	jx =  nx-1;
	jv = (e0-3)/8; if(jv<0) jv=0;
	q0 =  e0-8*(jv+1);

    /* set up f[0] to f[jx+jk] where f[jx+jk] = ipio2[jv+jk] */
	j = jv-jx; m = jx+jk;
	for(i=0;i<=m;i++,j++) f[i] = (j<0)? zero : (float) ipio2[j];

    /* compute q[0],q[1],...q[jk] */
	for (i=0;i<=jk;i++) {
	    for(j=0,fw=0.0;j<=jx;j++)
		fw += x[j]*f[jx+i-j];
	    q[i] = fw;
	}

	jz = jk;
recompute:
    /* distill q[] into iq[] reversingly */
	for(i=0,j=jz,z=q[jz];j>0;i++,j--) {
	    fw    =  (float)((int32_t)(twon8* z));
	    iq[i] =  (int32_t)(z-two8*fw);
	    z     =  q[j-1]+fw;
	}

    /* compute n */
	z  = __scalbnf(z,q0);		/* actual value of z */
	z -= (float)8.0*__floorf(z*(float)0.125);	/* trim off integer >= 8 */
	n  = (int32_t) z;
	z -= (float)n;
	ih = 0;
	if(q0>0) {	/* need iq[jz-1] to determine n */
	    i  = (iq[jz-1]>>(8-q0)); n += i;
	    iq[jz-1] -= i<<(8-q0);
	    ih = iq[jz-1]>>(7-q0);
	}
	else if(q0==0) ih = iq[jz-1]>>7;
	else if(z>=(float)0.5) ih=2;

	if(ih>0) {	/* q > 0.5 */
	    n += 1; carry = 0;
	    for(i=0;i<jz ;i++) {	/* compute 1-q */
		j = iq[i];
		if(carry==0) {
		    if(j!=0) {
			carry = 1; iq[i] = 0x100- j;
		    }
		} else  iq[i] = 0xff - j;
	    }
	    if(q0>0) {		/* rare case: chance is 1 in 12 */
	        switch(q0) {
	        case 1:
		   iq[jz-1] &= 0x7f; break;
		case 2:
		   iq[jz-1] &= 0x3f; break;
	        }
	    }
	    if(ih==2) {
		z = one - z;
		if(carry!=0) z -= __scalbnf(one,q0);
	    }
	}

    /* check if recomputation is needed */
	if(z==zero) {
	    j = 0;
	    for (i=jz-1;i>=jk;i--) j |= iq[i];
	    if(j==0) { /* need recomputation */
		/* On s390x gcc 6.1 -O3 produces the warning "array subscript is
		   below array bounds [-Werror=array-bounds]".  Only
		   __ieee754_rem_pio2f calls __kernel_rem_pio2f for normal
		   numbers and |x| ~> 2^7*(pi/2).  Thus x can't be zero and
		   ipio2 is not zero, too.  Thus not all iq[] values can't be
		   zero.  */
		DIAG_PUSH_NEEDS_COMMENT;
		DIAG_IGNORE_NEEDS_COMMENT (6.1, "-Warray-bounds");
		for(k=1;iq[jk-k]==0;k++);   /* k = no. of terms needed */
		DIAG_POP_NEEDS_COMMENT;

		for(i=jz+1;i<=jz+k;i++) {   /* add q[jz+1] to q[jz+k] */
		    f[jx+i] = (float) ipio2[jv+i];
		    for(j=0,fw=0.0;j<=jx;j++) fw += x[j]*f[jx+i-j];
		    q[i] = fw;
		}
		jz += k;
		goto recompute;
	    }
	}

    /* chop off zero terms */
	if(z==(float)0.0) {
	    jz -= 1; q0 -= 8;
	    while(iq[jz]==0) { jz--; q0-=8;}
	} else { /* break z into 8-bit if necessary */
	    z = __scalbnf(z,-q0);
	    if(z>=two8) {
		fw = (float)((int32_t)(twon8*z));
		iq[jz] = (int32_t)(z-two8*fw);
		jz += 1; q0 += 8;
		iq[jz] = (int32_t) fw;
	    } else iq[jz] = (int32_t) z ;
	}

    /* convert integer "bit" chunk to floating-point value */
	fw = __scalbnf(one,q0);
	for(i=jz;i>=0;i--) {
	    q[i] = fw*(float)iq[i]; fw*=twon8;
	}

    /* compute PIo2[0,...,jp]*q[jz,...,0] */
	for(i=jz;i>=0;i--) {
	    for(fw=0.0,k=0;k<=jp&&k<=jz-i;k++) fw += PIo2[k]*q[i+k];
	    fq[jz-i] = fw;
	}

    /* compress fq[] into y[] */
	switch(prec) {
	    case 0:
		fw = 0.0;
		for (i=jz;i>=0;i--) fw += fq[i];
		y[0] = (ih==0)? fw: -fw;
		break;
	    case 1:
	    case 2:;
		float fv = 0.0;
		for (i=jz;i>=0;i--) fv = math_narrow_eval (fv + fq[i]);
		y[0] = (ih==0)? fv: -fv;
		/* GCC mainline (to be GCC 9), as of 2018-05-22 on
		   i686, warns that fq[0] may be used uninitialized.
		   This is not possible because jz is always
		   nonnegative when the above loop initializing fq is
		   executed, because the result is never zero to full
		   precision (this function is not called for zero
		   arguments).  */
		DIAG_PUSH_NEEDS_COMMENT;
		DIAG_IGNORE_NEEDS_COMMENT (9, "-Wmaybe-uninitialized");
		fv = math_narrow_eval (fq[0]-fv);
		DIAG_POP_NEEDS_COMMENT;
		for (i=1;i<=jz;i++) fv = math_narrow_eval (fv + fq[i]);
		y[1] = (ih==0)? fv: -fv;
		break;
	    case 3:	/* painful */
		for (i=jz;i>0;i--) {
		    float fv = math_narrow_eval (fq[i-1]+fq[i]);
		    fq[i]  += fq[i-1]-fv;
		    fq[i-1] = fv;
		}
		for (i=jz;i>1;i--) {
		    float fv = math_narrow_eval (fq[i-1]+fq[i]);
		    fq[i]  += fq[i-1]-fv;
		    fq[i-1] = fv;
		}
		for (fw=0.0,i=jz;i>=2;i--) fw += fq[i];
		if(ih==0) {
		    y[0] =  fq[0]; y[1] =  fq[1]; y[2] =  fw;
		} else {
		    y[0] = -fq[0]; y[1] = -fq[1]; y[2] = -fw;
		}
	}
	return n&7;
}