ISO/ IEC JTC1/SC22/WG14 N750

* Document Number: WG14 N750/J11 97-113
 C9X Revision Proposal
 =====================
* Title: LIA-1 Binding: LIA-1 annex.
 Author: Fred J. Tydeman
 Author Affiliation: Tydeman Consulting
 Postal Address: 3711 Del Robles Dr., Austin, Texas, USA, 78727
 E-mail Address: tydeman@tybor.com
 Telephone Number: +1 (512) 255-8696
 Fax Number: +1 (512) 255-8696
 Sponsor: WG14
 Date: 1997年09月16日
 Proposal Category:
 __ Editorial change/non-normative contribution
 __ Correction
 Y_ New feature
 __ Addition to obsolescent feature list
 __ Addition to Future Directions
 __ Other (please specify) ______________________________
 Area of Standard Affected:
 __ Environment
 Y_ Language
 __ Preprocessor
 __ Library
 __ Macro/typedef/tag name
 __ Function
 __ Header
 Y_ Other (please specify) Annex_________________________
 Prior Art: Very little. Sun, and maybe others, print messages
 at program termination if any IEC 559 flags are raised. That
 is one small part of this proposal.
 Target Audience: Programmers writing programs that perform a
 significant amount of numeric processing.___________________
 Related Documents (if any):
 WG14/N758 C9X and LIA-1 informative annex,
 WG14/N756 LIA-1 Binding: Arithmetic exception => SIGFPE,
 WG14/N755 LIA-1 Binding: <fenv.h> to <stdmath.h>,
 WG14/N753 LIA-1 Binding: Rationale,
 WG14/N752 LIA-1 Binding: Optional parts annex,
 WG14/N751 LIA-1 Binding: Combined LIA-1 + IEC-559 annex,
 WG14/N749 LIA-1 Binding: <stdlia.h>,
 WG14/N748 LIA-1 Binding: Adding 'pole' from LIA-2,
 WG14/N747 IEC 559 Binding: Signaling NaNs,
 WG14/N528 C Binding for LIA-1,
 WG14/N488 LIA-2 (math library),
 WG14/N487 LIA-1 (arithmetic),
 WG14/N486 LIA Overview,
 WG14/N463 Impact of adding LIA-1,
 WG14/N461 C Binding of LIA-1
 Proposal Attached: _Y Yes __ No, but what's your interest?
 Abstract: This part of the C9X+LIA binding discusses the
 binding of LIA-1 to C, that is, what it takes to have a LIA-1
 conformant implementation.
 Proposal:
 Note: The '*' characters in the lefthand column are not part
 of the proposal (they are useful for emacs M-x outline mode)
 In the following, bold text, italic text,
 <TT>code sample</TT> are the conventions used to indicate
 text different from normal.
* -- Add to 6.8.8 Predefined macro names:
 The following macro name is defined if and only if the
 implementation conforms to Annex H.
 __STDC_LIA_1__ The decimal constant 1.
* -- Modify annex H Language Independent Arithmetic.
 Either replace with or merge the following.
 Annex H
 (normative)
 Language Independent Arithmetic
** H.1 Introduction
 -Replace the introduction with:
 This annex specifies C language support for the ISO/IEC
 10967-1 language independent arithmetic (LIA-1) standard.
 An implementation that defines __STDC_LIA_1__ conforms to
 the specification in this annex. Where a binding between
 the C language and LIA-1 is indicated, the LIA-1-specified
 behavior is adopted by reference, unless stated otherwise.
 An implementation shall conform to all the requirements of
 LIA-1 (ISO 10967-1:1994) unless otherwise specified in this
 clause.
 LIA-1 specifies a parameterized model of arithmetic
 computation. The purpose of LIA-1 is to provide a known
 environment in conforming implementations across platforms
 and languages for applications requiring numeric
 computation. Overall, the C binding of LIA-1 doesn't affect
 existing programs but new programs will achieve a higher
 degree of portability on LIA-1 systems. The impact of the
 changes are: adding some macros, adding a handful of library
 functions, detecting arithmetic exceptions, and requiring
 the implementation to document certain features of its
 arithmetic.
 -Replace LIA-1-like with LIA-1 throughout the annex.
** H.2 Types
*** H.2.2 Integral Types
 -Replace no integer types conform with:
 The C integral types int, long, long
 long, unsigned int, unsigned long,
 unsigned long long conform to LIA-1[footnote].
 [footnote]: The conformity of short and char
 (plain, signed or unsigned) is not relevant since values of
 these types are promoted to int (plain, signed or
 unsigned) before computations are done.
**** H.2.2.1 Integer Parameters
 -Add another parameter:
 modulo INT_OUT_OF_BOUNDS.
 The parameter modulo is always true for the unsigned types,
 and is not provided for those types. The parameter modulo
 is true when INT_OUT_OF_BOUNDS is 1 (wrap) or false when
 INT_OUT_OF_BOUNDS is 2 (notify) and covers all LIA-1
 conformant signed types. The implementation picks the value
 of modulo. It is implementation defined if the user can
 change the value of modulo.
**** H.2.2.2 Integer Operations
 -Add the following operations:
 modaI modulo(x, y), lmodulo(x, y), llmodulo(x, y).
 modpI No binding.
 signI sgn(x), lsgn(x), llsgn(x).
*** H.2.3 Floating-Point Types
 -Replace no floating-point types conform with:
 The floating types float, double, and long
 double conform to LIA-1.
**** H.2.3.1 Floating-Point Parameters
 -Add some more parameters:
 denorm FLT_SUBNORMAL, DBL_SUBNORMAL, LDBL_SUBNORMAL.
 iec_559 FLT_IEC_559, DBL_IEC_559, LDBL_IEC_559.
 The *_IEC_559 macros represent booleans and have values 1 or
 0.
 -Add some more derived constants:
 fmin FLT_TRUE_MIN, DBL_TRUE_MIN, LDBL_TRUE_MIN.
 rnd_error FLT_RND_ERR.
 If *_SUBNORMAL is not 1, then *_TRUE_MIN is the same as
 *_MIN.
 The FLT_RND_ERR macro must be less than or equal to 1.0
 Rounding error FLT_RND_ERR depends upon rounding mode
 FLT_ROUNDS. Rounding error will be constant
 expression suitable for use in #if if and only if
 FLT_ROUNDS is constant.
**** H.2.3.2 Floating-Point Operations
 -Add additional operations as functions:
 signF fsgnf(x), fsgn(x), fsgnl(x).
 fractionF fracrepf(x), fracrep(x), fracrepl(x).
 succF fsuccf(x), fsucc(x), fsuccl(x).
 predF fpredf(x), fpred(x), fprecl(x).
 ulpF ulpf(x), ulp(x), ulpl(x).
 truncF trunctof(x, n), truncto(x, n), trunctol(x, n).
 roundF roundtof(x, n), roundto(x, n), roundtol(x, n).
*** H.2.4 Type Conversions
 -Add the following macro calls:
 cvtF->I icvt(x), lcvt(x), llcvt(x),
 uicvt(x), ulcvt(x), ulcvt(x).
** H.3 Notification
**** H.3.1.1 Indicators
 -Split the 'undefined' into undefined and pole for the
 existing floating-point indicators.
 -Add the following:
 The following integer indicators shall be provided. They
 shall be clear at the start of the program. They are set
 when any arithmetic operation returns an exceptional value
 as defined in LIA-1 clause 5. Once set, an indicator shall
 be cleared only by explicit action of the program (that is,
 they are sticky).
 undefined INT_INVALID.
 pole INT_DIVBYZERO.
 integer_overflow INT_OVERFLOW.
 Undefined covers zero/zero, while pole covers finite
 non-zero/zero. For implementations that cannot distinguish
 the two cases, pole is used. The macros 
 DISTINGUISH_INT_DIV_BY_ZERO and DISTINGUISH_FP_DIV_BY_ZERO
 are the means to indicate if zero/zero can be distinguished
 from finite non-zero/zero for integral types and floating-point
 types respectively. The use of pole is a deviation from LIA-1.
 The macro FP2INT_OF_LARGE is used, in place of INT_OVERFLOW
 as required by LIA-1, to document how conversion of large
 floating-point values to out-of-bounds integral values will
 notify. FP2INT_OF_LARGE shall be either INT_OVERFLOW or
 FE_INVALID.
 For example, the LIA-1 indicator subset
 {floating_overflow, underflow, integer_overflow}
 would be denoted by the expression
 FE_OVERFLOW | FE_UNDERFLOW | INT_OVERFLOW
 The integer indicator interrogation and manipulation
 operations are:
 set_indicators ieraiseexcept(i).
 clear_indicators ieclearexcept(i).
 test_indicators ietestexcept(i).
 current_indicators ietestexcept(INT_ALL_EXCEPT).
 where i is an expression of type int representing a
 LIA-1 indicator subset.
 When notification via flags is chosen, then whenever a LIA-1
 exceptional value would result, the appropriate indicator
 shall be set (sometime before program accesses the status
 flag or terminates) and an implementation defined
 continuation value used.
 At program termination, if any LIA-1 indicator is set:
 - the implementation shall send an unambiguous and "hard to
 ignore" message (see LIA-1 subclause 6.1.2) to stderr. The
 message should identify the indicators set.
 - next, the stderr stream shall then be flushed and
 stderr closed. It is implementation defined if other
 open output streams are flushed, other open streams closed,
 and any files created by the tmpfile function are
 removed.
 - finally, control is returned to the host environment. An
 implementation-defined form of the status unsuccessful
 termination is returned.
**** H.3.1.2 Traps
 Trap first exception and terminate shall include the
 following.
 When notification via traps is chosen, then whenever a LIA-1
 exceptional value would result, the implementation shall
 send a message to stderr (sometime before any other
 output). The message sent to stderr should identify
 the cause of the notification and the operation responsible.
 Next, the stderr stream shall then be flushed and
 stderr closed. It is implementation defined if other
 open output streams are flushed, other open streams closed,
 and any files created by the tmpfile function are removed.
 Finally, control is returned to the host environment. An
 implementation-defined form of the status unsuccessful
 termination is returned.
*** H.3.2 User selection
 The implementation shall provide a means for a user or
 program to select among the alternative notification
 mechanisms provided (see LIA-1 subclause 6.3). The
 LIA_NOTIFY pragma is the method used. LIA_NOTIFY FLAGS and
 LIA_NOTIFY TRAP are the LIA-1 required conformant
 mechanisms. LIA_NOTIFY UNDEF and LIA_NOTIFY IGNORE are not
 LIA-1 conformant.
** H.4 <stdlia.h>
 This subclause contains specification of <stdlia.h> facilities
 that is required for LIA-1 implementations.
*** H.4.1 Nearest integer macros
 The macros used to convert from floating-point types to
 signed integral types are defined for out-of-bounds results
 in both wrapping and trapping modes. The use of
 FP2INT_OF_LARGE instead of INT_OVERFLOW is a deviation from
 LIA-1.
**** H.4.1.1 The icvt macro
 If the rounded value is outside the range of int and
 INT_OUT_OF_BOUNDS is 1 (wrap), the rounded value is
 wrapped modulo (INT_MAX-INT_MIN+1).
 If the rounded value is outside the range of int and
 INT_OUT_OF_BOUNDS is 2 (notify), the numeric result
 is unspecified and FP2INT_OF_LARGE is raised.
**** H.4.1.2 The lcvt macro
 If the rounded value is outside the range of long and
 INT_OUT_OF_BOUNDS is 1 (wrap), the rounded value is
 wrapped modulo (LONG_MAX-LONG_MIN+1).
 If the rounded value is outside the range of long and
 INT_OUT_OF_BOUNDS is 2 (notify), the numeric result
 is unspecified and FP2INT_OF_LARGE is raised.
**** H.4.1.3 The llcvt macro
 If the rounded value is outside the range of long
 long and INT_OUT_OF_BOUNDS is 1 (wrap), the
 rounded value is wrapped modulo
 (LLONG_MAX-LLONG_MIN+1).
 If the rounded value is outside the range of long
 long and INT_OUT_OF_BOUNDS is 2 (notify), the
 numeric result is unspecified and FP2INT_OF_LARGE is
 raised.
*** H.4.2 Modulo functions
**** H.4.2.1 The modulo function
 modulo(i,0) raises INT_INVALID and returns an
 unspecified value
**** H.4.2.2 The lmodulo function
 lmodulo(i,0) raises INT_INVALID and returns an
 unspecified value
**** H.4.2.3 The llmodulo function
 llmodulo(i,0) raises INT_INVALID and returns an
 unspecified value