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Teach libc's compat ldexp stub to raise fp exceptions. 

This ldexp stub will shadow the ldexp weak alias for scalbn in libm,
which is unfortunate but hard to fix properly without chasing the
mythical libc bump beast.  With the change here, we should raise all
the same exceptions that libm's scalbn does -- overflow, underflow,
inexact-result, and (for signalling NaN only) invalid-operation.
This in turn should correct the missing overflow/underflow exceptions
of our portable C fma, and perhaps other routines.

XXX pullup
This commit is contained in:
riastradh 2020-05-21 05:56:31 +00:00
parent f0f145987a
commit 59ccc04e14
1 changed files with 37 additions and 24 deletions
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61
lib/libc/compat/gen/compat_ldexp_ieee754.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: compat_ldexp_ieee754.c,v 1.7 2016/08/27 09:35:13 christos Exp $ */
/* $NetBSD: compat_ldexp_ieee754.c,v 1.8 2020/05/21 05:56:31 riastradh Exp $ */
/*-
* Copyright (c) 1999 The NetBSD Foundation, Inc.
@ -31,14 +31,34 @@
#include <sys/cdefs.h>
#if defined(LIBC_SCCS) && !defined(lint)
__RCSID("$NetBSD: compat_ldexp_ieee754.c,v 1.7 2016/08/27 09:35:13 christos Exp $");
__RCSID("$NetBSD: compat_ldexp_ieee754.c,v 1.8 2020/05/21 05:56:31 riastradh Exp $");
#endif /* LIBC_SCCS and not lint */
#include <sys/types.h>
#include <machine/ieee.h>
#include <errno.h>
double ldexp(double, int);
#include <machine/ieee.h>
#include <errno.h>
#include <float.h>
#include <math.h>
static volatile const double tiny = DBL_MIN, huge = DBL_MAX;
static double
underflow(double val)
{
errno = ERANGE;
return (val < 0 ? -tiny*tiny : tiny*tiny);
}
static double
overflow(double val)
{
errno = ERANGE;
return (val < 0 ? -huge*huge : huge*huge);
}
/*
* Multiply the given value by 2^expon.
@ -53,10 +73,13 @@ ldexp(double val, int expon)
oldexp = u.dblu_dbl.dbl_exp;
/*
* If input is zero, Inf or NaN, just return it.
* If input is zero, Inf or NaN, just return it, but raise
* invalid exception if it is a signalling NaN: adding any of
* these inputs to itself gives itself as output; arithmetic on
* a signalling NaN additionally raises invalid-operation.
*/
if (u.dblu_d == 0.0 || oldexp == DBL_EXP_INFNAN)
return (val);
return (val + val);
if (oldexp == 0) {
/*
@ -68,17 +91,13 @@ ldexp(double val, int expon)
* Optimization: if the scaling can be done in a single
* multiply, or underflows, just do it now.
*/
if (expon <= -DBL_FRACBITS) {
errno = ERANGE;
return (val < 0.0 ? -0.0 : 0.0);
}
if (expon <= -DBL_FRACBITS)
return underflow(val);
mul.dblu_d = 0.0;
mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS;
u.dblu_d *= mul.dblu_d;
if (u.dblu_d == 0.0) {
errno = ERANGE;
return (val < 0.0 ? -0.0 : 0.0);
}
if (u.dblu_d == 0.0)
return underflow(val);
return (u.dblu_d);
} else {
/*
@ -105,20 +124,14 @@ ldexp(double val, int expon)
/*
* The result overflowed; return +/-Inf.
*/
u.dblu_dbl.dbl_exp = DBL_EXP_INFNAN;
u.dblu_dbl.dbl_frach = 0;
u.dblu_dbl.dbl_fracl = 0;
errno = ERANGE;
return (u.dblu_d);
return overflow(val);
} else if (newexp <= 0) {
/*
* The output number is either denormal or underflows (see
* comments in machine/ieee.h).
*/
if (newexp <= -DBL_FRACBITS) {
errno = ERANGE;
return (val < 0.0 ? -0.0 : 0.0);
}
if (newexp <= -DBL_FRACBITS)
return underflow(val);
/*
* Denormalize the result. We do this with a multiply. If
* expon is very large, it won't fit in a double, so we have