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Document some libm error handling intents.

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Joseph Myers 2013-11-28 16:52:36 +00:00
parent 3c1c46a64a
commit c5df760908
2 changed files with 25 additions and 7 deletions
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@ -1,5 +1,12 @@
2013-11-28 Joseph Myers <joseph@codesourcery.com>
* manual/arith.texi (FP Exceptions): Document that exceptions may
not be raised when matherr is used.
(Math Error Reporting): Document overflow in directed rounding
modes. Document that errno may not be set when finite values are
returned on overflow. Document intent to set errno on underflow
only for underflow to zero.
[BZ #16271]
* sysdeps/ieee754/dbl-64/e_sqrt.c (__ieee754_sqrt): Set
round-to-nearest then adjust result for other rounding modes.

25
manual/arith.texi
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@ -497,7 +497,8 @@ In the System V math library, the user-defined function @code{matherr}
is called when certain exceptions occur inside math library functions.
However, the Unix98 standard deprecates this interface. We support it
for historical compatibility, but recommend that you do not use it in
new programs.
new programs. When this interface is used, exceptions may not be
raised.
@noindent
The exceptions defined in @w{IEEE 754} are:
@ -806,7 +807,8 @@ an integer. Do not attempt to modify an @code{fexcept_t} variable.
Many of the math functions are defined only over a subset of the real or
complex numbers. Even if they are mathematically defined, their result
may be larger or smaller than the range representable by their return
type. These are known as @dfn{domain errors}, @dfn{overflows}, and
type without loss of accuracy. These are known as @dfn{domain errors},
@dfn{overflows}, and
@dfn{underflows}, respectively. Math functions do several things when
one of these errors occurs. In this manual we will refer to the
complete response as @dfn{signalling} a domain error, overflow, or
@ -816,11 +818,20 @@ When a math function suffers a domain error, it raises the invalid
exception and returns NaN. It also sets @var{errno} to @code{EDOM};
this is for compatibility with old systems that do not support @w{IEEE
754} exception handling. Likewise, when overflow occurs, math
functions raise the overflow exception and return @math{@infinity{}} or
@math{-@infinity{}} as appropriate. They also set @var{errno} to
@code{ERANGE}. When underflow occurs, the underflow exception is
raised, and zero (appropriately signed) is returned. @var{errno} may be
set to @code{ERANGE}, but this is not guaranteed.
functions raise the overflow exception and, in the default rounding
mode, return @math{@infinity{}} or @math{-@infinity{}} as appropriate
(in other rounding modes, the largest finite value of the appropriate
sign is returned when appropriate for that rounding mode). They also
set @var{errno} to @code{ERANGE} if returning @math{@infinity{}} or
@math{-@infinity{}}; @var{errno} may or may not be set to
@code{ERANGE} when a finite value is returned on overflow. When
underflow occurs, the underflow exception is raised, and zero
(appropriately signed) or a subnormal value, as appropriate for the
mathematical result of the function and the rounding mode, is
returned. @var{errno} may be set to @code{ERANGE}, but this is not
guaranteed; it is intended that @theglibc{} should set it when the
underflow is to an appropriately signed zero, but not necessarily for
other underflows.
Some of the math functions are defined mathematically to result in a
complex value over parts of their domains. The most familiar example of