From owner-freebsd-bugs Thu Jun 13 12:40:19 2002 Delivered-To: freebsd-bugs@hub.freebsd.org Received: from freefall.freebsd.org (freefall.FreeBSD.org [216.136.204.21]) by hub.freebsd.org (Postfix) with ESMTP id 1D6D237B422 for ; Thu, 13 Jun 2002 12:40:02 -0700 (PDT) Received: (from gnats@localhost) by freefall.freebsd.org (8.11.6/8.11.6) id g5DJe2669588; Thu, 13 Jun 2002 12:40:02 -0700 (PDT) (envelope-from gnats) Received: from nwww.freebsd.org (www.FreeBSD.org [216.136.204.117]) by hub.freebsd.org (Postfix) with ESMTP id BAB0337B40E for ; Thu, 13 Jun 2002 12:30:49 -0700 (PDT) Received: from www.freebsd.org (localhost [127.0.0.1]) by nwww.freebsd.org (8.12.2/8.12.2) with ESMTP id g5DJUnhG084578 for ; Thu, 13 Jun 2002 12:30:49 -0700 (PDT) (envelope-from nobody@www.freebsd.org) Received: (from nobody@localhost) by www.freebsd.org (8.12.2/8.12.2/Submit) id g5DJUn0x084577; Thu, 13 Jun 2002 12:30:49 -0700 (PDT) Message-Id: <200206131930.g5DJUn0x084577@www.freebsd.org> Date: Thu, 13 Jun 2002 12:30:49 -0700 (PDT) From: Stephen L Moshier To: freebsd-gnats-submit@FreeBSD.org X-Send-Pr-Version: www-1.0 Subject: misc/39236: error in e_pow.c Sender: owner-freebsd-bugs@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org >Number: 39236 >Category: misc >Synopsis: error in e_pow.c >Confidential: no >Severity: non-critical >Priority: medium >Responsible: freebsd-bugs >State: open >Quarter: >Keywords: >Date-Required: >Class: sw-bug >Submitter-Id: current-users >Arrival-Date: Thu Jun 13 12:40:01 PDT 2002 >Closed-Date: >Last-Modified: >Originator: Stephen L Moshier >Release: any >Organization: >Environment: >Description: pow(x,y) returns 0 when x is very close to -1.0 and y is very large. >How-To-Repeat: The following test program prints pow(1.0000000000000002e+00 4.5035996273704970e+15) = 2.7182818284590455e+00 pow(-1.0000000000000002e+00 4.5035996273704970e+15) = 0.0000000000000000e+00 pow(9.9999999999999978e-01 4.5035996273704970e+15) = 3.6787944117144222e-01 pow(-9.9999999999999978e-01 4.5035996273704970e+15) = 0.0000000000000000e+00 which is incorrect for the negative arguments raised to an odd integer power. double pow (double, double); int main () { double x, y, z; x = 1.0 + pow (2.0, -52.0); y = 1.0 + pow (2.0, 52.0); z = pow (x, y); printf ("pow(%.16e %.16e) = %.16e\n", x, y, z); x = -x; z = pow (x, y); printf ("pow(%.16e %.16e) = %.16e\n", x, y, z); x = 1.0 - pow (2.0, -52.0); z = pow (x, y); printf ("pow(%.16e %.16e) = %.16e\n", x, y, z); x = -x; z = pow (x, y); printf ("pow(%.16e %.16e) = %.16e\n", x, y, z); } >Fix: freebsd: src/lib/msun/src/e_pow.c *** e_pow.c 1999/07/13 23:49:20 1.1 --- e_pow.c 2002/06/13 17:06:57 *************** *** 224,230 **** if(ix>0x3ff00000) return (hy>0)? C[4]*C[4]:C[5]*C[5]; /* now |1-x| is tiny <= 2**-20, suffice to compute log(x) by x-x^2/2+x^3/3-x^4/4 */ ! t = x-1; /* t has 20 trailing zeros */ w = (t*t)*(0.5-t*(0.3333333333333333333333-t*0.25)); u = C[25]*t; /* ivln2_h has 21 sig. bits */ v = t*C[26]-w*C[24]; --- 224,230 ---- if(ix>0x3ff00000) return (hy>0)? C[4]*C[4]:C[5]*C[5]; /* now |1-x| is tiny <= 2**-20, suffice to compute log(x) by x-x^2/2+x^3/3-x^4/4 */ ! t = ax-1; /* t has 20 trailing zeros */ w = (t*t)*(0.5-t*(0.3333333333333333333333-t*0.25)); u = C[25]*t; /* ivln2_h has 21 sig. bits */ v = t*C[26]-w*C[24]; >Release-Note: >Audit-Trail: >Unformatted: To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-bugs" in the body of the message