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Tests for module 'modf-ieee'.
* modules/modf-ieee-tests: New file.
* tests/test-modf-ieee.c: New file.

author | Bruno Haible <bruno@clisp.org> |
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date | Sun, 26 Feb 2012 17:55:21 +0100 |

parents | a712776b11ce |

children | 4e33322b32f8 |

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@node Integer Properties @section Integer Properties @c Copyright (C) 2011-2012 Free Software Foundation, Inc. @c Permission is granted to copy, distribute and/or modify this document @c under the terms of the GNU Free Documentation License, Version 1.3 or @c any later version published by the Free Software Foundation; with no @c Invariant Sections, with no Front-Cover Texts, and with no Back-Cover @c Texts. A copy of the license is included in the ``GNU Free @c Documentation License'' file as part of this distribution. @c Written by Paul Eggert. @cindex integer properties The @code{intprops} module consists of an include file @code{<intprops.h>} that defines several macros useful for testing properties of integer types. @cindex integer overflow @cindex overflow, integer Integer overflow is a common source of problems in programs written in C and other languages. In some cases, such as signed integer arithmetic in C programs, the resulting behavior is undefined, and practical platforms do not always behave as if integers wrap around reliably. In other cases, such as unsigned integer arithmetic in C, the resulting behavior is well-defined, but programs may still misbehave badly after overflow occurs. Many techniques have been proposed to attack these problems. These include precondition testing, GCC's @option{-ftrapv} option, GCC's no-undefined-overflow branch, the As-if Infinitely Ranged (AIR) model implemented in Clang, saturation semantics where overflow reliably yields an extreme value, the RICH static transformer to an overflow-checking variant, and special testing methods. For more information about these techniques, see: Dannenberg R, Dormann W, Keaton D @emph{et al.}, @url{http://www.sei.cmu.edu/library/abstracts/reports/10tn008.cfm, As-if Infinitely Ranged integer model -- 2nd ed.}, Software Engineering Institute Technical Note CMU/SEI-2010-TN-008, April 2010. Gnulib supports the precondition testing technique, as this is easy to support portably. There are two families of precondition tests: the first, for integer ranges, has a simple and straightforward implementation, while the second, for integer types, is easier to use. @menu * Integer Type Determination:: Whether a type has integer properties. * Integer Bounds:: Bounds on integer values and representations. * Integer Range Overflow:: Integer overflow checking if bounds are known. * Integer Type Overflow:: General integer overflow checking. @end menu @node Integer Type Determination @subsection Integer Type Determination @findex TYPE_IS_INTEGER @code{TYPE_IS_INTEGER (@var{t})} expands to a constant expression that is 1 if the arithmetic type @var{t} is an integer type. @code{_Bool} counts as an integer type. @findex TYPE_SIGNED @code{TYPE_SIGNED (@var{t})} expands to a constant expression that is 1 if the arithmetic type @var{t} is a signed integer type or a floating type. If @var{t} is an integer type, @code{TYPE_SIGNED (@var{t})} expands to an integer constant expression. Example usage: @example #include <intprops.h> #include <time.h> enum @{ time_t_is_signed_integer = TYPE_IS_INTEGER (time_t) && TYPE_SIGNED (time_t) @}; @end example @node Integer Bounds @subsection Integer Bounds @cindex integer bounds @findex INT_BUFSIZE_BOUND @code{INT_BUFSIZE_BOUND (@var{t})} expands to an integer constant expression that is a bound on the size of the string representing an integer type or expression @var{t} in decimal notation, including the terminating null character and any leading @code{-} character. For example, if @code{INT_STRLEN_BOUND (int)} is 12, any value of type @code{int} can be represented in 12 bytes or less, including the terminating null. The bound is not necessarily tight. Example usage: @example #include <intprops.h> #include <stdio.h> int int_strlen (int i) @{ char buf[INT_BUFSIZE_BOUND (int)]; return sprintf (buf, "%d", i); @} @end example @findex INT_STRLEN_BOUND @code{INT_STRLEN_BOUND (@var{t})} expands to an integer constant expression that is a bound on the length of the string representing an integer type or expression @var{t} in decimal notation, including any leading @code{-} character. This is one less than @code{INT_BUFSIZE_BOUND (@var{t})}. @findex TYPE_MINIMUM @findex TYPE_MAXIMUM @code{TYPE_MINIMUM (@var{t})} and @code{TYPE_MAXIMUM (@var{t})} expand to integer constant expressions equal to the minimum and maximum values of the integer type @var{t}. These expressions are of the type @var{t} (or more precisely, the type @var{t} after integer promotions). Example usage: @example #include <stdint.h> #include <sys/types.h> #include <intprops.h> int in_off_t_range (intmax_t a) @{ return TYPE_MINIMUM (off_t) <= a && a <= TYPE_MAXIMUM (off_t); @} @end example @node Integer Range Overflow @subsection Integer Range Overflow @cindex integer range overflow @cindex overflow, integer range These macros yield 1 if the corresponding C operators might not yield numerically correct answers due to arithmetic overflow. They do not rely on undefined or implementation-defined behavior. They expand to integer constant expressions if their arguments are. Their implementations are simple and straightforward, but they are typically harder to use than the integer type overflow macros. @xref{Integer Type Overflow}. Although the implementation of these macros is similar to that suggested in Seacord R, The CERT C Secure Coding Standard (2009, revised 2011), in its two sections ``@url{https://www.securecoding.cert.org/confluence/display/seccode/INT30-C.+Ensure+that+unsigned+integer+operations+do+not+wrap, INT30-C. Ensure that unsigned integer operations do not wrap}'' and ``@url{https://www.securecoding.cert.org/confluence/display/seccode/INT32-C.+Ensure+that+operations+on+signed+integers+do+not+result+in+overflow, INT32-C. Ensure that operations on signed integers do not result in overflow}'', Gnulib's implementation was derived independently of CERT's suggestions. Example usage: @example #include <intprops.h> void print_product (long int a, long int b) @{ if (INT_MULTIPLY_RANGE_OVERFLOW (a, b, LONG_MIN, LONG_MAX)) printf ("multiply would overflow"); else printf ("product is %ld", a * b); @} @end example @noindent These macros have the following restrictions: @itemize @bullet @item Their arguments must be integer expressions. @item They may evaluate their arguments zero or multiple times, so the arguments should not have side effects. @item The arithmetic arguments (including the @var{min} and @var{max} arguments) must be of the same integer type after the usual arithmetic conversions, and the type must have minimum value @var{min} and maximum @var{max}. Unsigned values should use a zero @var{min} of the proper type, for example, @code{(unsigned int) 0}. @end itemize These macros are tuned for constant @var{min} and @var{max}. For commutative operations such as @code{@var{a} + @var{b}}, they are also tuned for constant @var{b}. @table @code @item INT_ADD_RANGE_OVERFLOW (@var{a}, @var{b}, @var{min}, @var{max}) @findex INT_ADD_RANGE_OVERFLOW Yield 1 if @code{@var{a} + @var{b}} would overflow in [@var{min},@var{max}] integer arithmetic. See above for restrictions. @item INT_SUBTRACT_RANGE_OVERFLOW (@var{a}, @var{b}, @var{min}, @var{max}) @findex INT_SUBTRACT_RANGE_OVERFLOW Yield 1 if @code{@var{a} - @var{b}} would overflow in [@var{min},@var{max}] integer arithmetic. See above for restrictions. @item INT_NEGATE_RANGE_OVERFLOW (@var{a}, @var{min}, @var{max}) @findex INT_NEGATE_RANGE_OVERFLOW Yield 1 if @code{-@var{a}} would overflow in [@var{min},@var{max}] integer arithmetic. See above for restrictions. @item INT_MULTIPLY_RANGE_OVERFLOW (@var{a}, @var{b}, @var{min}, @var{max}) @findex INT_MULTIPLY_RANGE_OVERFLOW Yield 1 if @code{@var{a} * @var{b}} would overflow in [@var{min},@var{max}] integer arithmetic. See above for restrictions. @item INT_DIVIDE_RANGE_OVERFLOW (@var{a}, @var{b}, @var{min}, @var{max}) @findex INT_DIVIDE_RANGE_OVERFLOW Yield 1 if @code{@var{a} / @var{b}} would overflow in [@var{min},@var{max}] integer arithmetic. See above for restrictions. Division overflow can happen on two's complement hosts when dividing the most negative integer by @minus{}1. This macro does not check for division by zero. @item INT_REMAINDER_RANGE_OVERFLOW (@var{a}, @var{b}, @var{min}, @var{max}) @findex INT_REMAINDER_RANGE_OVERFLOW Yield 1 if @code{@var{a} % @var{b}} would overflow in [@var{min},@var{max}] integer arithmetic. See above for restrictions. Remainder overflow can happen on two's complement hosts when dividing the most negative integer by @minus{}1; although the mathematical result is always 0, in practice some implementations trap, so this counts as an overflow. This macro does not check for division by zero. @item INT_LEFT_SHIFT_RANGE_OVERFLOW (@var{a}, @var{b}, @var{min}, @var{max}) @findex INT_LEFT_SHIFT_RANGE_OVERFLOW Yield 1 if @code{@var{a} << @var{b}} would overflow in [@var{min},@var{max}] integer arithmetic. See above for restrictions. Here, @var{min} and @var{max} are for @var{a} only, and @var{b} need not be of the same type as the other arguments. The C standard says that behavior is undefined for shifts unless 0@leq{}@var{b}<@var{w} where @var{w} is @var{a}'s word width, and that when @var{a} is negative then @code{@var{a} << @var{b}} has undefined behavior and @code{@var{a} >> @var{b}} has implementation-defined behavior, but this macro does not check these other restrictions. @end table @node Integer Type Overflow @subsection Integer Type Overflow @cindex integer type overflow @cindex overflow, integer type These macros yield 1 if the corresponding C operators might not yield numerically correct answers due to arithmetic overflow of an integer type. They work correctly on all known practical hosts, and do not rely on undefined behavior due to signed arithmetic overflow. They expand to integer constant expressions if their arguments are. They are easier to use than the integer range overflow macros (@pxref{Integer Range Overflow}). Example usage: @example #include <intprops.h> void print_product (long int a, long int b) @{ if (INT_MULTIPLY_OVERFLOW (a, b)) printf ("multiply would overflow"); else printf ("product is %ld", a * b); @} @end example @noindent These macros have the following restrictions: @itemize @bullet @item Their arguments must be integer expressions. @item They may evaluate their arguments zero or multiple times, so the arguments should not have side effects. @end itemize These macros are tuned for their last argument being a constant. @table @code @item INT_ADD_OVERFLOW (@var{a}, @var{b}) @findex INT_ADD_OVERFLOW Yield 1 if @code{@var{a} + @var{b}} would overflow. See above for restrictions. @item INT_SUBTRACT_OVERFLOW (@var{a}, @var{b}) @findex INT_SUBTRACT_OVERFLOW Yield 1 if @code{@var{a} - @var{b}} would overflow. See above for restrictions. @item INT_NEGATE_OVERFLOW (@var{a}) @findex INT_NEGATE_OVERFLOW Yields 1 if @code{-@var{a}} would overflow. See above for restrictions. @item INT_MULTIPLY_OVERFLOW (@var{a}, @var{b}) @findex INT_MULTIPLY_OVERFLOW Yield 1 if @code{@var{a} * @var{b}} would overflow. See above for restrictions. @item INT_DIVIDE_OVERFLOW (@var{a}, @var{b}) @findex INT_DIVIDE_OVERFLOW Yields 1 if @code{@var{a} / @var{b}} would overflow. See above for restrictions. Division overflow can happen on two's complement hosts when dividing the most negative integer by @minus{}1. This macro does not check for division by zero. @item INT_REMAINDER_OVERFLOW (@var{a}, @var{b}) @findex INT_REMAINDER_OVERFLOW Yield 1 if @code{@var{a} % @var{b}} would overflow. See above for restrictions. Remainder overflow can happen on two's complement hosts when dividing the most negative integer by @minus{}1; although the mathematical result is always 0, in practice some implementations trap, so this counts as an overflow. This macro does not check for division by zero. @item INT_LEFT_SHIFT_OVERFLOW (@var{a}, @var{b}) @findex INT_LEFT_SHIFT_OVERFLOW Yield 1 if @code{@var{a} << @var{b}} would overflow. See above for restrictions. The C standard says that behavior is undefined for shifts unless 0@leq{}@var{b}<@var{w} where @var{w} is @var{a}'s word width, and that when @var{a} is negative then @code{@var{a} << @var{b}} has undefined behavior and @code{@var{a} >> @var{b}} has implementation-defined behavior, but this macro does not check these other restrictions. @end table