Date:	Tue, 6 Oct 1998 13:33:20 +0300 (IDT)
From:	Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
X-Sender:	eliz AT is
To:	Kbwms AT aol DOT com, djgpp-workers AT delorie DOT com
Subject:	Re: Troubles Compiling the Test Programs
In-Reply-To:	<Pine.SUN.3.91.981004123119.1863G-100000@is>
Message-ID:	<Pine.SUN.3.91.981006132651.16991D-100000@is>
MIME-Version:	1.0
Reply-To:	djgpp-workers AT delorie DOT com

On Sun, 4 Oct 1998, I wrote:

> Can anybody see what's wrong in the latest alpha?

Well, I know what's wrong ;-).  It's the same GCC optimizations strike 
again.  Here are the offending lines from s_rint.c:

                w = TWO52[sx]+x;
                t = w-TWO52[sx];

When GCC sees this, it optimizes w out of existence, and sets t = x.  And 
that is wrong, since this trick reveals the current rounding mode of the 
FPU, and `rint' really needs that.

The following patches correct this and several similar code snippets 
elsewhere in the library by declaring crucial variables `volatile'.  
(These changes removed several inaccuracies reported by the Cygnus test 
suite, so it's probably more here than meets the eye.)

*** src/libm/math/s_rint.c~1	Sat Feb  7 14:13:28 1998
--- src/libm/math/s_rint.c	Sun Oct  4 19:39:54 1998
*************** TWO52[2]={
*** 44,50 ****
  {
  	__int32_t i0,j_0,sx;
  	__uint32_t i,i1;
! 	double w,t;
  	EXTRACT_WORDS(i0,i1,x);
  	sx = (i0>>31)&1;
  	j_0 = ((i0>>20)&0x7ff)-0x3ff;
--- 44,55 ----
  {
  	__int32_t i0,j_0,sx;
  	__uint32_t i,i1;
! 	/* w is volatile so GCC doesn't optimize it out of existence
! 	   when it sees that w = x + 2^52 and t = w - 2^52.  We need
! 	   that computation unoptimized because it reveals the current
! 	   rounding mode.  */
! 	volatile double w;
! 	double t;
  	EXTRACT_WORDS(i0,i1,x);
  	sx = (i0>>31)&1;
  	j_0 = ((i0>>20)&0x7ff)-0x3ff;
*** src/libm/math/sf_rint.c~1	Sat Feb  7 14:13:20 1998
--- src/libm/math/sf_rint.c	Sun Oct  4 19:39:46 1998
*************** TWO23[2]={
*** 34,40 ****
  {
  	__int32_t i0,j_0,sx;
  	__uint32_t i,i1;
! 	float w,t;
  	GET_FLOAT_WORD(i0,x);
  	sx = (i0>>31)&1;
  	j_0 = ((i0>>23)&0xff)-0x7f;
--- 34,45 ----
  {
  	__int32_t i0,j_0,sx;
  	__uint32_t i,i1;
! 	/* w is volatile so GCC doesn't optimize it out of existence
! 	   when it sees that w = x + 2^23 and t = w - 2^23.  We need
! 	   that computation unoptimized because it reveals the current
! 	   rounding mode.  */
! 	volatile float w;
! 	float t;
  	GET_FLOAT_WORD(i0,x);
  	sx = (i0>>31)&1;
  	j_0 = ((i0>>23)&0xff)-0x7f;
*** src/libm/math/e_sqrt.c~1	Sat Feb  7 13:47:36 1998
--- src/libm/math/e_sqrt.c	Sun Oct  4 19:44:34 1998
*************** static	double	one	= 1.0, tiny=1.0e-300;
*** 98,104 ****
  	double x;
  #endif
  {
! 	double z;
  	__int32_t sign = (int)0x80000000U; 
  	__uint32_t r,t1,s1,ix1,q1;
  	__int32_t ix0,s0,q,m,t,i;
--- 98,104 ----
  	double x;
  #endif
  {
! 	volatile double z;	/* so that GCC will never optimize it away */
  	__int32_t sign = (int)0x80000000U; 
  	__uint32_t r,t1,s1,ix1,q1;
  	__int32_t ix0,s0,q,m,t,i;
*** src/libm/math/ef_sqrt.c~1	Sat Feb  7 14:13:24 1998
--- src/libm/math/ef_sqrt.c	Sun Oct  4 19:53:42 1998
*************** static	float	one	= 1.0, tiny=1.0e-30;
*** 28,34 ****
  	float x;
  #endif
  {
! 	float z;
  	__int32_t 	sign = (int)0x80000000U; 
  	__uint32_t r;
  	__int32_t ix,s,q,m,t,i;
--- 28,34 ----
  	float x;
  #endif
  {
! 	volatile float z;	/* to prevent GCC from optimizing it away */
  	__int32_t 	sign = (int)0x80000000U; 
  	__uint32_t r;
  	__int32_t ix,s,q,m,t,i;
*** src/libm/math/s_log1p.c~1	Fri Sep 18 16:44:32 1998
--- src/libm/math/s_log1p.c	Sun Oct  4 19:49:52 1998
*************** static double zero = 0.0;
*** 153,159 ****
  	double x;
  #endif
  {
! 	double hfsq,f=0.0,c=0.0,s,z,R,u;
  	__int32_t k,hx,hu=0.0,ax;
  
  	GET_HIGH_WORD(hx,x);
--- 153,160 ----
  	double x;
  #endif
  {
! 	double hfsq,f=0.0,c=0.0,s,z,R;
! 	volatile double u;	/* so GCC never optimizes it away */
  	__int32_t k,hx,hu=0.0,ax;
  
  	GET_HIGH_WORD(hx,x);
*** src/libm/math/sf_log1p.c~1	Fri Sep 18 16:52:44 1998
--- src/libm/math/sf_log1p.c	Sun Oct  4 19:54:32 1998
*************** static float zero = 0.0;
*** 44,50 ****
  	float x;
  #endif
  {
! 	float hfsq,f=0.0,c=0.0,s,z,R,u;
  	__int32_t k,hx,hu=0.0,ax;
  
  	GET_FLOAT_WORD(hx,x);
--- 44,51 ----
  	float x;
  #endif
  {
! 	float hfsq,f=0.0,c=0.0,s,z,R;
! 	volatile float u;	/* so GCC doesn't optimize it away */
  	__int32_t k,hx,hu=0.0,ax;
  
  	GET_FLOAT_WORD(hx,x);
*** src/libm/math/e_pow.c~1	Sat Feb  7 13:47:38 1998
--- src/libm/math/e_pow.c	Sun Oct  4 20:35:36 1998
*************** ivln2_l  =  1.92596299112661746887e-08; 
*** 104,110 ****
  	double x, y;
  #endif
  {
! 	double z,ax,z_h,z_l,p_h,p_l;
  	double y_1,t1,t2,r,s,t,u,v,w;
  	__int32_t i,j,k,yisint,n;
  	__int32_t hx,hy,ix,iy;
--- 104,111 ----
  	double x, y;
  #endif
  {
! 	volatile double z;	/* prevent GCC from optimizing it away */
! 	double ax,z_h,z_l,p_h,p_l;
  	double y_1,t1,t2,r,s,t,u,v,w;
  	__int32_t i,j,k,yisint,n;
  	__int32_t hx,hy,ix,iy;
*** src/libm/math/ef_pow.c~1	Sat Feb  7 14:13:24 1998
--- src/libm/math/ef_pow.c	Sun Oct  4 20:36:56 1998
*************** ivln2_l  =  7.0526075433e-06; /* 0x36eca
*** 63,69 ****
  	float x, y;
  #endif
  {
! 	float z,ax,z_h,z_l,p_h,p_l;
  	float y_1,t1,t2,r,s,t,u,v,w;
  	__int32_t i,j,k,yisint,n;
  	__int32_t hx,hy,ix,iy,is;
--- 63,70 ----
  	float x, y;
  #endif
  {
! 	volatile float z;	/* prevent optimizing it out of existence */
! 	float ax,z_h,z_l,p_h,p_l;
  	float y_1,t1,t2,r,s,t,u,v,w;
  	__int32_t i,j,k,yisint,n;
  	__int32_t hx,hy,ix,iy,is;
*** src/libm/math/e_rem_pio2.c~1	Sat Feb  7 13:47:38 1998
--- src/libm/math/e_rem_pio2.c	Sun Oct  4 20:41:58 1998
*************** pio2_3t =  8.47842766036889956997e-32; /
*** 89,95 ****
  	double x,y[];
  #endif
  {
! 	double z=0.0,w,t,r,fn;
  	double tx[3];
  	__int32_t i,j,n,ix,hx;
  	int e0,nx;
--- 89,96 ----
  	double x,y[];
  #endif
  {
! 	volatile double z=0.0,r; /* prevent optimizing out of existence */
! 	double w,t,fn;
  	double tx[3];
  	__int32_t i,j,n,ix,hx;
  	int e0,nx;
*** src/libm/math/ef_rem_pio2.c~1	Sat Jun 27 16:53:48 1998
--- src/libm/math/ef_rem_pio2.c	Sun Oct  4 20:43:32 1998
*************** pio2_3t =  6.1232342629e-17; /* 0x248d31
*** 102,108 ****
  	float x,y[];
  #endif
  {
! 	float z,w,t,r,fn;
  	float tx[3];
  	__int32_t i,j,n,ix,hx;
  	int e0,nx;
--- 102,109 ----
  	float x,y[];
  #endif
  {
! 	volatile float z,r;	/* prevent optimizing out of existence */
! 	float w,t,fn;
  	float tx[3];
  	__int32_t i,j,n,ix,hx;
  	int e0,nx;
*** src/libm/math/k_cos.c~1	Tue Apr 15 08:39:48 1997
--- src/libm/math/k_cos.c	Sun Oct  4 20:57:20 1998
*************** C6  = -1.13596475577881948265e-11; /* 0x
*** 70,76 ****
  	double x,y;
  #endif
  {
! 	double a,hz,z,r,qx;
  	__int32_t ix;
  	GET_HIGH_WORD(ix,x);
  	ix &= 0x7fffffff;			/* ix = |x|'s high word*/
--- 70,77 ----
  	double x,y;
  #endif
  {
! 	volatile double hz;	/* prevent optimizing out of existence */
! 	double a,z,r,qx;
  	__int32_t ix;
  	GET_HIGH_WORD(ix,x);
  	ix &= 0x7fffffff;			/* ix = |x|'s high word*/
*** src/libm/math/kf_cos.c~1	Tue Apr 15 08:39:48 1997
--- src/libm/math/kf_cos.c	Sun Oct  4 21:01:54 1998
*************** C6  = -1.1359647598e-11; /* 0xad47d74e *
*** 35,41 ****
  	float x,y;
  #endif
  {
! 	float a,hz,z,r,qx;
  	__int32_t ix;
  	GET_FLOAT_WORD(ix,x);
  	ix &= 0x7fffffff;			/* ix = |x|'s high word*/
--- 35,42 ----
  	float x,y;
  #endif
  {
! 	volatile float hz;	/* prevent optimizing out of existence */
! 	float a,z,r,qx;
  	__int32_t ix;
  	GET_FLOAT_WORD(ix,x);
  	ix &= 0x7fffffff;			/* ix = |x|'s high word*/

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