Re: compiling newlib

Keith Packard via Newlib <[email protected]> Tue, 25 Aug 2020 10:04:18 -0700

Newsgroups	gmane.comp.lib.newlib
Message-ID	<[email protected]>

Paul Zimmermann <[email protected]> writes:

> thank you Jeff for your answer.
>
> In return I found I believe an issue with newlib's tgammaf function, for
> input -0, where it gives +inf instead of -inf:

Yeah, it's easy to fix the underlying __ieee754_lgamma functions to
adjust the sign of the return:

There's a bit of a mess with the gamma functions. There are _r
versions of these functions that pass through the sign return pointer
instead of applying it locally as they should. That reduces the set of
gamma functions as follows:

Reentrant functions:

        double                  float
        __ieee754_lgamma_r      __ieee754_lgammaf_r
        __ieee754_gamma         __ieee754_gammaf

        lgamma_r                lgammaf_r
        tgamma                  tgammaf

gamma/gammaf should be alternate names for tgamma/tgammaf, and would
thus be re-entrant.

Non-reentrant functions:

        __ieee754_lgamma        __ieee754_lgammaf        

        lgamma                  lgammaf

-- 
-keith

0001-libm-Fix-sign-value-returned-from-__ieee754_lgamma-_.patch (text/x-diff, 1.5 KB)

From 0cba5165a7f6cd69aca95bf82a9f1437bfa144dc Mon Sep 17 00:00:00 2001
From: Keith Packard <[email protected]>
Date: Tue, 25 Aug 2020 09:32:35 -0700
Subject: [PATCH] libm: Fix sign value returned from __ieee754_lgamma*_r(-0)

The sign of the INFINITY returned from these cases needs to match the
sign of the zero.

Signed-off-by: Keith Packard <[email protected]>
---
 newlib/libm/math/er_lgamma.c  | 6 +++++-
 newlib/libm/math/erf_lgamma.c | 6 +++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/newlib/libm/math/er_lgamma.c b/newlib/libm/math/er_lgamma.c
index 386a8a73b..36408382f 100644
--- a/newlib/libm/math/er_lgamma.c
+++ b/newlib/libm/math/er_lgamma.c
@@ -225,7 +225,11 @@ static double zero=  0.00000000000000000000e+00;
 	*signgamp = 1;
 	ix = hx&0x7fffffff;
 	if(ix>=0x7ff00000) return x*x;
-	if((ix|lx)==0) return one/zero;
+	if((ix|lx)==0) {
+	    if(hx<0)
+	        *signgamp = -1;
+	    return one/zero;
+	}
 	if(ix<0x3b900000) {	/* |x|<2**-70, return -log(|x|) */
 	    if(hx<0) {
 	        *signgamp = -1;
diff --git a/newlib/libm/math/erf_lgamma.c b/newlib/libm/math/erf_lgamma.c
index 3c6ba02af..a45423949 100644
--- a/newlib/libm/math/erf_lgamma.c
+++ b/newlib/libm/math/erf_lgamma.c
@@ -160,7 +160,11 @@ static float zero=  0.0000000000e+00;
 	*signgamp = 1;
 	ix = hx&0x7fffffff;
 	if(ix>=0x7f800000) return x*x;
-	if(ix==0) return one/zero;
+	if(ix==0) {
+	    if(hx<0)
+	        *signgamp = -1;
+	    return one/zero;
+	}
 	if(ix<0x1c800000) {	/* |x|<2**-70, return -log(|x|) */
 	    if(hx<0) {
 	        *signgamp = -1;
-- 
2.28.0

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