From 3374868668e708581ca06e256f6122518c89a8ad Mon Sep 17 00:00:00 2001
From: Vineet Gupta <vgupta@synopsys.com>
Date: Fri, 29 May 2020 15:21:39 -0700
Subject: [PATCH] ieee754: provide gcc builtins based generic sqrt functions

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
---
 sysdeps/generic/math-use-builtins.h  |  3 +++
 sysdeps/ieee754/dbl-64/e_sqrt.c      |  6 ++++++
 sysdeps/ieee754/flt-32/e_sqrtf.c     | 16 ++++++++++------
 sysdeps/s390/fpu/math-use-builtins.h |  3 +++
 4 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/sysdeps/generic/math-use-builtins.h b/sysdeps/generic/math-use-builtins.h
index 8a39ef5..fc724c8 100644
--- a/sysdeps/generic/math-use-builtins.h
+++ b/sysdeps/generic/math-use-builtins.h
@@ -60,4 +60,7 @@
 # define USE_COPYSIGNF128_BUILTIN 0
 #endif
 
+#define USE_SQRT_BUILTIN 0
+#define USE_SQRTF_BUILTIN 0
+
 #endif /* math-use-builtins.h */
diff --git a/sysdeps/ieee754/dbl-64/e_sqrt.c b/sysdeps/ieee754/dbl-64/e_sqrt.c
index d42a1a4..518a8ae 100644
--- a/sysdeps/ieee754/dbl-64/e_sqrt.c
+++ b/sysdeps/ieee754/dbl-64/e_sqrt.c
@@ -41,6 +41,7 @@
 #include <math_private.h>
 #include <fenv_private.h>
 #include <libm-alias-finite.h>
+#include <math-use-builtins.h>
 
 /*********************************************************************/
 /* An ultimate sqrt routine. Given an IEEE double machine number x   */
@@ -50,6 +51,10 @@
 double
 __ieee754_sqrt (double x)
 {
+#if USE_SQRT_BUILTIN
+  return __builtin_sqrt (x);
+#else
+  /* Use generic implementation.  */
   static const double
     rt0 = 9.99999999859990725855365213134618E-01,
     rt1 = 4.99999999495955425917856814202739E-01,
@@ -138,6 +143,7 @@ __ieee754_sqrt (double x)
 	return (x - x) / (x - x); /* sqrt(-ve)=sNaN */
       return 0x1p-256 * __ieee754_sqrt (x * 0x1p512);
     }
+#endif /* ! USE_SQRT_BUILTIN  */
 }
 #ifndef __ieee754_sqrt
 libm_alias_finite (__ieee754_sqrt, __sqrt)
diff --git a/sysdeps/ieee754/flt-32/e_sqrtf.c b/sysdeps/ieee754/flt-32/e_sqrtf.c
index b339444..177bf5d 100644
--- a/sysdeps/ieee754/flt-32/e_sqrtf.c
+++ b/sysdeps/ieee754/flt-32/e_sqrtf.c
@@ -16,12 +16,15 @@
 #include <math.h>
 #include <math_private.h>
 #include <libm-alias-finite.h>
-
-static	const float	one	= 1.0, tiny=1.0e-30;
+#include <math-use-builtins.h>
 
 float
 __ieee754_sqrtf(float x)
 {
+#if USE_SQRTF_BUILTIN
+	return __builtin_sqrtf (x);
+#else
+	/* Use generic implementation.  */
 	float z;
 	int32_t sign = (int)0x80000000;
 	int32_t ix,s,q,m,t,i;
@@ -70,10 +73,10 @@ __ieee754_sqrtf(float x)
 
     /* use floating add to find out rounding direction */
 	if(ix!=0) {
-	    z = one-tiny; /* trigger inexact flag */
-	    if (z>=one) {
-		z = one+tiny;
-		if (z>one)
+	    z = 0x1p0 - 0x1.4484cp-100; /* trigger inexact flag.  */
+	    if (z >= 0x1p0) {
+		z = 0x1p0 + 0x1.4484cp-100;
+		if (z > 0x1p0)
 		    q += 2;
 		else
 		    q += (q&1);
@@ -83,6 +86,7 @@ __ieee754_sqrtf(float x)
 	ix += (m <<23);
 	SET_FLOAT_WORD(z,ix);
 	return z;
+#endif /* ! USE_SQRTF_BUILTIN  */
 }
 #ifndef __ieee754_sqrtf
 libm_alias_finite (__ieee754_sqrtf, __sqrtf)
diff --git a/sysdeps/s390/fpu/math-use-builtins.h b/sysdeps/s390/fpu/math-use-builtins.h
index db00c3a..eb87b6b 100644
--- a/sysdeps/s390/fpu/math-use-builtins.h
+++ b/sysdeps/s390/fpu/math-use-builtins.h
@@ -108,4 +108,7 @@
 # define USE_COPYSIGNF128_BUILTIN 0
 #endif
 
+#define USE_SQRT_BUILTIN 0
+#define USE_SQRTF_BUILTIN 0
+
 #endif /* math-use-builtins.h */
-- 
2.7.4