Patchwork Update libquadmath from GLIBC

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Submitter Tobias Burnus
Date Oct. 31, 2012, 12:06 p.m.
Message ID <50911455.8060902@net-b.de>
Download mbox | patch
Permalink /patch/195858/
State New
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Comments

Tobias Burnus - Oct. 31, 2012, 12:06 p.m.
Hi all,

libquadmath's math functions are based on (but not identical to) GLIBC's 
sysdeps/ieee754/ldbl-128 functions. In the attached patch, I have ported 
the bug fixes from GLIBC over to libquadmath. Hopefully, the port is 
complete and correct.

I intent to commit the patch soon, unless there are other comments or 
suggestions.

(It was build and tested on x86-64-gnu-linux. Unfortunately, we do not 
have a test suite for it, except for two minor tests in gfortran.dg.)

Tobias
Richard Guenther - Oct. 31, 2012, 12:13 p.m.
On Wed, Oct 31, 2012 at 1:06 PM, Tobias Burnus <burnus@net-b.de> wrote:
> Hi all,
>
> libquadmath's math functions are based on (but not identical to) GLIBC's
> sysdeps/ieee754/ldbl-128 functions.

Heh, last time I copied things from sysdeps/ieee754 into GCC rms objected
and I had to revert ... (libgccmath).

Richard.

> In the attached patch, I have ported the
> bug fixes from GLIBC over to libquadmath. Hopefully, the port is complete
> and correct.
>
> I intent to commit the patch soon, unless there are other comments or
> suggestions.
>
> (It was build and tested on x86-64-gnu-linux. Unfortunately, we do not have
> a test suite for it, except for two minor tests in gfortran.dg.)
>
> Tobias

Patch

2012-10-31  Tobias Burnus  <burnus@net-b.de>
	    Joseph Myers <joseph@codesourcery.com>
	    David S. Miller <davem@davemloft.net>
	    Ulrich Drepper <drepper@redhat.com>
	    Marek Polacek <polacek@redhat.com>:
	    Petr Baudis <pasky@suse.cz>

	* math/expm1q.c (expm1q): Changes from GLIBC. Use expq for
	large parameters. Fix errno for boundary conditions.
	* math/finiteq.c (finiteq): Add comment.
	* math/fmaq.c (fmaq): Changes from GLIBC. Fix missing underflows
	and bad results for some subnormal results. Fix sign of inexact
	zero return. Fix sign of exact zero return.
	Ensure additions are not scheduled after fetestexcept.
	* math/jnq.c (jnq): Changes from GLIBC. Set up errno properly
	for ynq. Fix jnq precision.
	* math/nearbyintq.c (nearbyintq): Changes from GLIBC. Do not
	manipulate bits before adding and subtracting TWO112[sx].
	* math/rintq.c (rintq): Ditto.
	* math/scalbnq.c (scalbnq): Changes from GLIBC. Fix integer
	overflow.

diff --git a/libquadmath/math/expm1q.c b/libquadmath/math/expm1q.c
index 510c98f..cd254b5 100644
--- a/libquadmath/math/expm1q.c
+++ b/libquadmath/math/expm1q.c
@@ -53,6 +53,7 @@ 
 
 
 
+#include <errno.h>
 #include "quadmath-imp.h"
 
 /* exp(x) - 1 = x + 0.5 x^2 + x^3 P(x)/Q(x)
@@ -100,6 +101,11 @@  expm1q (__float128 x)
   ix = u.words32.w0;
   sign = ix & 0x80000000;
   ix &= 0x7fffffff;
+  if (!sign && ix >= 0x40060000)
+    {
+      /* If num is positive and exp >= 6 use plain exp.  */
+      return expq (x);
+    }
   if (ix >= 0x7fff0000)
     {
       /* Infinity. */
@@ -120,7 +126,10 @@  expm1q (__float128 x)
 
   /* Overflow.  */
   if (x > maxlog)
-    return (HUGE_VALQ * HUGE_VALQ);
+    {
+      __set_errno (ERANGE);
+      return (HUGE_VALQ * HUGE_VALQ);
+    }
 
   /* Minimum value.  */
   if (x < minarg)
diff --git a/libquadmath/math/finiteq.c b/libquadmath/math/finiteq.c
index f22e9d7..663c928 100644
--- a/libquadmath/math/finiteq.c
+++ b/libquadmath/math/finiteq.c
@@ -15,6 +15,11 @@ 
 
 #include "quadmath-imp.h"
 
+/*
+ * finiteq(x) returns 1 is x is finite, else 0;
+ * no branching!
+ */
+
 int
 finiteq (const __float128 x)
 {
diff --git a/libquadmath/math/fmaq.c b/libquadmath/math/fmaq.c
index 126b0a2..cd1b232 100644
--- a/libquadmath/math/fmaq.c
+++ b/libquadmath/math/fmaq.c
@@ -1,5 +1,5 @@ 
 /* Compute x * y + z as ternary operation.
-   Copyright (C) 2010 Free Software Foundation, Inc.
+   Copyright (C) 2010-2012 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Jakub Jelinek <jakub@redhat.com>, 2010.
 
@@ -57,6 +57,11 @@  fmaq (__float128 x, __float128 y, __float128 z)
 	  && u.ieee.exponent != 0x7fff
           && v.ieee.exponent != 0x7fff)
 	return (z + x) + y;
+      /* If z is zero and x are y are nonzero, compute the result
+	 as x * y to avoid the wrong sign of a zero result if x * y
+	 underflows to 0.  */
+      if (z == 0 && x != 0 && y != 0)
+	return x * y;
       /* If x or y or z is Inf/NaN, or if fma will certainly overflow,
 	 or if x * y is less than half of FLT128_DENORM_MIN,
 	 compute as x * y + z.  */
@@ -136,6 +141,11 @@  fmaq (__float128 x, __float128 y, __float128 z)
       y = v.value;
       z = w.value;
     }
+
+  /* Ensure correct sign of exact 0 + 0.  */
+  if (__builtin_expect ((x == 0 || y == 0) && z == 0, 0))
+    return x * y + z;
+
   /* Multiplication m1 + m2 = x * y using Dekker's algorithm.  */
 #define C ((1LL << (FLT128_MANT_DIG + 1) / 2) + 1)
   __float128 x1 = x * C;
@@ -191,7 +201,7 @@  fmaq (__float128 x, __float128 y, __float128 z)
 #endif
       v.value = a1 + u.value;
       /* Ensure the addition is not scheduled after fetestexcept call.  */
-      asm volatile ("" : : "m" (v));
+      asm volatile ("" : : "m" (v.value));
 #ifdef USE_FENV_H
       int j = fetestexcept (FE_INEXACT) != 0;
       feupdateenv (&env);
@@ -220,20 +230,14 @@  fmaq (__float128 x, __float128 y, __float128 z)
 	{
 	  /* v.ieee.mant_low & 2 is LSB bit of the result before rounding,
 	     v.ieee.mant_low & 1 is the round bit and j is our sticky
-	     bit.  In round-to-nearest 001 rounds down like 00,
-	     011 rounds up, even though 01 rounds down (thus we need
-	     to adjust), 101 rounds down like 10 and 111 rounds up
-	     like 11.  */
-	  if ((v.ieee.mant_low & 3) == 1)
-	    {
-	      v.value *= 0x1p-226Q;
-	      if (v.ieee.negative)
-		return v.value - 0x1p-16494Q /* __FLT128_DENORM_MIN__ */;
-	      else
-		return v.value + 0x1p-16494Q /* __FLT128_DENORM_MIN__ */;
-	    }
-	  else
-	    return v.value * 0x1p-226Q;
+	     bit. */
+	  w.value = 0.0Q;
+	  w.ieee.mant_low = ((v.ieee.mant_low & 3) << 1) | j;
+	  w.ieee.negative = v.ieee.negative;
+	  v.ieee.mant_low &= ~3U;
+	  v.value *= 0x1p-226Q;
+	  w.value *= 0x1p-2Q;
+	  return v.value + w.value;
 	}
       v.ieee.mant_low |= j;
       return v.value * 0x1p-226Q;
diff --git a/libquadmath/math/jnq.c b/libquadmath/math/jnq.c
index d82947a..3a10fc5 100644
--- a/libquadmath/math/jnq.c
+++ b/libquadmath/math/jnq.c
@@ -11,9 +11,9 @@ 
 
 /* Modifications for 128-bit long double are
    Copyright (C) 2001 Stephen L. Moshier <moshier@na-net.ornl.gov>
-   and are incorporated herein by permission of the author.  The author 
+   and are incorporated herein by permission of the author.  The author
    reserves the right to distribute this material elsewhere under different
-   copying permissions.  These modifications are distributed here under 
+   copying permissions.  These modifications are distributed here under
    the following terms:
 
     This library is free software; you can redistribute it and/or
@@ -56,6 +56,7 @@ 
  *
  */
 
+#include <errno.h>
 #include "quadmath-imp.h"
 
 static const __float128
@@ -273,7 +274,16 @@  jnq (int n, __float128 x)
 		    }
 		}
 	    }
-	  b = (t * j0q (x) / b);
+	  /* j0() and j1() suffer enormous loss of precision at and
+	   * near zero; however, we know that their zero points never
+	   * coincide, so just choose the one further away from zero.
+	   */
+	  z = j0q (x);
+	  w = j1q (x);
+	  if (fabsq (z) >= fabsq (w))
+	    b = (t * z / b);
+	  else
+	    b = (t * w / a);
 	}
     }
   if (sgn == 1)
@@ -374,6 +384,9 @@  ynq (int n, __float128 x)
 	  a = temp;
 	}
     }
+  /* If B is +-Inf, set up errno accordingly.  */
+  if (! finiteq (b))
+    __set_errno (ERANGE);
   if (sign > 0)
     return b;
   else
diff --git a/libquadmath/math/nearbyintq.c b/libquadmath/math/nearbyintq.c
index 8e92c5a..2071248 100644
--- a/libquadmath/math/nearbyintq.c
+++ b/libquadmath/math/nearbyintq.c
@@ -44,18 +44,13 @@  nearbyintq(__float128 x)
 	fenv_t env;
 #endif
 	int64_t i0,j0,sx;
-	uint64_t i,i1;
+	uint64_t i1;
 	__float128 w,t;
 	GET_FLT128_WORDS64(i0,i1,x);
 	sx = (((uint64_t)i0)>>63);
 	j0 = ((i0>>48)&0x7fff)-0x3fff;
-	if(j0<48) {
+	if(j0<112) {
 	    if(j0<0) {
-		if(((i0&0x7fffffffffffffffLL)|i1)==0) return x;
-		i1 |= (i0&0x0000ffffffffffffLL);
-		i0 &= 0xffffe00000000000ULL;
-		i0 |= ((i1|-i1)>>16)&0x0000800000000000LL;
-		SET_FLT128_MSW64(x,i0);
 #ifdef USE_FENV_H
 		feholdexcept (&env);
 #endif
@@ -67,25 +62,11 @@  nearbyintq(__float128 x)
 		GET_FLT128_MSW64(i0,t);
 		SET_FLT128_MSW64(t,(i0&0x7fffffffffffffffLL)|(sx<<63));
 	        return t;
-	    } else {
-		i = (0x0000ffffffffffffLL)>>j0;
-		if(((i0&i)|i1)==0) return x; /* x is integral */
-		i>>=1;
-		if(((i0&i)|i1)!=0) {
-		    if(j0==47) i1 = 0x4000000000000000ULL; else
-		    i0 = (i0&(~i))|((0x0000200000000000LL)>>j0);
-		}
 	    }
-	} else if (j0>111) {
+	} else {
 	    if(j0==0x4000) return x+x;	/* inf or NaN */
 	    else return x;		/* x is integral */
-	} else {
-	    i = -1ULL>>(j0-48);
-	    if((i1&i)==0) return x;	/* x is integral */
-	    i>>=1;
-	    if((i1&i)!=0) i1 = (i1&(~i))|((0x4000000000000000LL)>>(j0-48));
 	}
-	SET_FLT128_WORDS64(x,i0,i1);
 #ifdef USE_FENV_H
 	feholdexcept (&env);
 #endif
diff --git a/libquadmath/math/rintq.c b/libquadmath/math/rintq.c
index fe7a591..9c8ab40 100644
--- a/libquadmath/math/rintq.c
+++ b/libquadmath/math/rintq.c
@@ -13,6 +13,16 @@ 
  * ====================================================
  */
 
+/*
+ * rintq(x)
+ * Return x rounded to integral value according to the prevailing
+ * rounding mode.
+ * Method:
+ *	Using floating addition.
+ * Exception:
+ *	Inexact flag raised if x not equal to rintq(x).
+ */
+
 #include "quadmath-imp.h"
 
 static const __float128
@@ -32,35 +42,16 @@  rintq (__float128 x)
 	j0 = ((i0>>48)&0x7fff)-0x3fff;
 	if(j0<48) {
 	    if(j0<0) {
-		if(((i0&0x7fffffffffffffffLL)|i1)==0) return x;
-		i1 |= (i0&0x0000ffffffffffffLL);
-		i0 &= 0xffffe00000000000ULL;
-		i0 |= ((i1|-i1)>>16)&0x0000800000000000LL;
-		SET_FLT128_MSW64(x,i0);
 	        w = TWO112[sx]+x;
 	        t = w-TWO112[sx];
 		GET_FLT128_MSW64(i0,t);
 		SET_FLT128_MSW64(t,(i0&0x7fffffffffffffffLL)|(sx<<63));
 	        return t;
-	    } else {
-		i = (0x0000ffffffffffffLL)>>j0;
-		if(((i0&i)|i1)==0) return x; /* x is integral */
-		i>>=1;
-		if(((i0&i)|i1)!=0) {
-		    if(j0==47) i1 = 0x4000000000000000ULL; else
-		    i0 = (i0&(~i))|((0x0000200000000000LL)>>j0);
-		}
 	    }
-	} else if (j0>111) {
+	} else {
 	    if(j0==0x4000) return x+x;	/* inf or NaN */
 	    else return x;		/* x is integral */
-	} else {
-	    i = -1ULL>>(j0-48);
-	    if((i1&i)==0) return x;	/* x is integral */
-	    i>>=1;
-	    if((i1&i)!=0) i1 = (i1&(~i))|((0x4000000000000000LL)>>(j0-48));
 	}
-	SET_FLT128_WORDS64(x,i0,i1);
 	w = TWO112[sx]+x;
 	return w-TWO112[sx];
 }
diff --git a/libquadmath/math/scalblnq.c b/libquadmath/math/scalblnq.c
index 75997f6..b233225 100644
--- a/libquadmath/math/scalblnq.c
+++ b/libquadmath/math/scalblnq.c
@@ -13,6 +13,13 @@ 
  * ====================================================
  */
 
+/*
+ * scalblnq (_float128 x, long int n)
+ * scalblnq(x,n) returns x* 2**n  computed by  exponent
+ * manipulation rather than by actually performing an
+ * exponentiation or a multiplication.
+ */
+
 #include "quadmath-imp.h"
 
 static const __float128
@@ -34,10 +41,12 @@  scalblnq (__float128 x, long int n)
 	    k = ((hx>>48)&0x7fff) - 114;
 	}
         if (k==0x7fff) return x+x;		/* NaN or Inf */
-        k = k+n;
-        if (n> 50000 || k > 0x7ffe)
-	  return huge*copysignq(huge,x); /* overflow  */
 	if (n< -50000) return tiny*copysignq(tiny,x); /*underflow*/
+        if (n> 50000 || k+n > 0x7ffe)
+	  return huge*copysignq(huge,x); /* overflow  */
+	/* Now k and n are bounded we know that k = k+n does not
+	   overflow.  */
+        k = k+n;
         if (k > 0) 				/* normal result */
 	    {SET_FLT128_MSW64(x,(hx&0x8000ffffffffffffULL)|(k<<48)); return x;}
         if (k <= -114)
diff --git a/libquadmath/math/scalbnq.c b/libquadmath/math/scalbnq.c
index b7049a7..f0852ee 100644
--- a/libquadmath/math/scalbnq.c
+++ b/libquadmath/math/scalbnq.c
@@ -13,6 +13,14 @@ 
  * ====================================================
  */
 
+
+/*
+ * scalbnq (__float128 x, int n)
+ * scalbnq(x,n) returns x* 2**n  computed by  exponent
+ * manipulation rather than by actually performing an
+ * exponentiation or a multiplication.
+ */
+
 #include "quadmath-imp.h"
 
 static const __float128
@@ -34,10 +42,12 @@  scalbnq (__float128 x, int n)
 	    k = ((hx>>48)&0x7fff) - 114;
 	}
         if (k==0x7fff) return x+x;		/* NaN or Inf */
-        k = k+n;
-        if (n> 50000 || k > 0x7ffe)
-	  return huge*copysignq(huge,x); /* overflow  */
 	if (n< -50000) return tiny*copysignq(tiny,x); /*underflow*/
+        if (n> 50000 || k+n > 0x7ffe)
+	  return huge*copysignq(huge,x); /* overflow  */
+	/* Now k and n are bounded we know that k = k+n does not
+	   overflow.  */
+        k = k+n;
         if (k > 0) 				/* normal result */
 	    {SET_FLT128_MSW64(x,(hx&0x8000ffffffffffffULL)|(k<<48)); return x;}
         if (k <= -114)