gcc/doc/libgcc.texi

@c Copyright (C) 2003, 2004 Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.
@c Contributed by Aldy Hernandez <aldy@quesejoda.com>

@node Libgcc
@chapter The GCC low-level runtime library

GCC provides a low-level runtime library, @file{libgcc.a} or
@file{libgcc_s.so.1} on some platforms.  GCC generates calls to
routines in this library automatically, whenever it needs to perform
some operation that is too complicated to emit inline code for.

Most of the routines in @code{libgcc} handle arithmetic operations
that the target processor cannot perform directly.  This includes
integer multiply and divide on some machines, and all floating-point
operations on other machines.  @code{libgcc} also includes routines
for exception handling, and a handful of miscellaneous operations.

Some of these routines can be defined in mostly machine-independent C.
Others must be hand-written in assembly language for each processor
that needs them.

GCC will also generate calls to C library routines, such as
@code{memcpy} and @code{memset}, in some cases.  The set of routines
that GCC may possibly use is documented in @ref{Other
Builtins,,,gcc, Using the GNU Compiler Collection (GCC)}.

These routines take arguments and return values of a specific machine
mode, not a specific C type.  @xref{Machine Modes}, for an explanation
of this concept.  For illustrative purposes, in this chapter the
floating point type @code{float} is assumed to correspond to @code{SFmode};
@code{double} to @code{DFmode}; and @code{@w{long double}} to both
@code{TFmode} and @code{XFmode}.  Similarly, the integer types @code{int}
and @code{@w{unsigned int}} correspond to @code{SImode}; @code{long} and
@code{@w{unsigned long}} to @code{DImode}; and @code{@w{long long}} and
@code{@w{unsigned long long}} to @code{TImode}.

@menu
* Integer library routines::
* Soft float library routines::
* Exception handling routines::
* Miscellaneous routines::
@end menu

@node Integer library routines
@section Routines for integer arithmetic

The integer arithmetic routines are used on platforms that don't provide
hardware support for arithmetic operations on some modes.

@subsection Arithmetic functions

@deftypefn {Runtime Function} int __ashlsi3 (int @var{a}, int @var{b})
@deftypefnx {Runtime Function} long __ashldi3 (long @var{a}, int @var{b})
@deftypefnx {Runtime Function} {long long} __ashlti3 (long long @var{a}, int @var{b})
These functions return the result of shifting @var{a} left by @var{b} bits.
@end deftypefn

@deftypefn {Runtime Function} int __ashrsi3 (int @var{a}, int @var{b})
@deftypefnx {Runtime Function} long __ashrdi3 (long @var{a}, int @var{b})
@deftypefnx {Runtime Function} {long long} __ashrti3 (long long @var{a}, int @var{b})
These functions return the result of arithmetically shifting @var{a} right
by @var{b} bits.
@end deftypefn

@deftypefn {Runtime Function} int __divsi3 (int @var{a}, int @var{b})
@deftypefnx {Runtime Function} long __divdi3 (long @var{a}, long @var{b})
@deftypefnx {Runtime Function} {long long} __divti3 (long long @var{a}, long long @var{b})
These functions return the quotient of the signed division of @var{a} and
@var{b}.
@end deftypefn

@deftypefn {Runtime Function} int __lshrsi3 (int @var{a}, int @var{b})
@deftypefnx {Runtime Function} long __lshrdi3 (long @var{a}, int @var{b})
@deftypefnx {Runtime Function} {long long} __lshrti3 (long long @var{a}, int @var{b})
These functions return the result of logically shifting @var{a} right by
@var{b} bits.
@end deftypefn

@deftypefn {Runtime Function} int __modsi3 (int @var{a}, int @var{b})
@deftypefnx {Runtime Function} long __moddi3 (long @var{a}, long @var{b})
@deftypefnx {Runtime Function} {long long} __modti3 (long long @var{a}, long long @var{b})
These functions return the remainder of the signed division of @var{a}
and @var{b}.
@end deftypefn

@deftypefn {Runtime Function} int __mulsi3 (int @var{a}, int @var{b})
@deftypefnx {Runtime Function} long __muldi3 (long @var{a}, long @var{b})
@deftypefnx {Runtime Function} {long long} __multi3 (long long @var{a}, long long @var{b})
These functions return the product of @var{a} and @var{b}.
@end deftypefn

@deftypefn {Runtime Function} long __negdi2 (long @var{a})
@deftypefnx {Runtime Function} {long long} __negti2 (long long @var{a})
These functions return the negation of @var{a}.
@end deftypefn

@deftypefn {Runtime Function} {unsigned int} __udivsi3 (unsigned int @var{a}, unsigned int @var{b})
@deftypefnx {Runtime Function} {unsigned long} __udivdi3 (unsigned long @var{a}, unsigned long @var{b})
@deftypefnx {Runtime Function} {unsigned long long} __udivti3 (unsigned long long @var{a}, unsigned long long @var{b})
These functions return the quotient of the unsigned division of @var{a}
and @var{b}.
@end deftypefn

@deftypefn {Runtime Function} {unsigned long} __udivmoddi3 (unsigned long @var{a}, unsigned long @var{b}, unsigned long *@var{c})
@deftypefnx {Runtime Function} {unsigned long long} __udivti3 (unsigned long long @var{a}, unsigned long long @var{b}, unsigned long long *@var{c})
These functions calculate both the quotient and remainder of the unsigned
division of @var{a} and @var{b}.  The return value is the quotient, and
the remainder is placed in variable pointed to by @var{c}.
@end deftypefn

@deftypefn {Runtime Function} {unsigned int} __umodsi3 (unsigned int @var{a}, unsigned int @var{b})
@deftypefnx {Runtime Function} {unsigned long} __umoddi3 (unsigned long @var{a}, unsigned long @var{b})
@deftypefnx {Runtime Function} {unsigned long long} __umodti3 (unsigned long long @var{a}, unsigned long long @var{b})
These functions return the remainder of the unsigned division of @var{a}
and @var{b}.
@end deftypefn

@subsection Comparison functions

The following functions implement integral comparisons.  These functions
implement a low-level compare, upon which the higher level comparison
operators (such as less than and greater than or equal to) can be
constructed.  The returned values lie in the range zero to two, to allow
the high-level operators to be implemented by testing the returned
result using either signed or unsigned comparison.

@deftypefn {Runtime Function} int __cmpdi2 (long @var{a}, long @var{b})
@deftypefnx {Runtime Function} int __cmpti2 (long long @var{a}, long long @var{b})
These functions perform a signed comparison of @var{a} and @var{b}.  If
@var{a} is less than @var{b}, they return 0; if @var{a} is greater than
@var{b}, they return 2; and if @var{a} and @var{b} are equal they return 1.
@end deftypefn

@deftypefn {Runtime Function} int __ucmpdi2 (unsigned long @var{a}, unsigned long @var{b})
@deftypefnx {Runtime Function} int __ucmpti2 (unsigned long long @var{a}, unsigned long long @var{b})
These functions perform an unsigned comparison of @var{a} and @var{b}.
If @var{a} is less than @var{b}, they return 0; if @var{a} is greater than
@var{b}, they return 2; and if @var{a} and @var{b} are equal they return 1.
@end deftypefn

@subsection Trapping arithmetic functions

The following functions implement trapping arithmetic.  These functions
call the libc function @code{abort} upon signed arithmetic overflow.

@deftypefn {Runtime Function} int __absvsi2 (int @var{a})
@deftypefnx {Runtime Function} long __absvdi2 (long @var{a})
These functions return the absolute value of @var{a}.
@end deftypefn

@deftypefn {Runtime Function} int __addvsi3 (int @var{a}, int @var{b})
@deftypefnx {Runtime Function} long __addvdi3 (long @var{a}, long @var{b})
These functions return the sum of @var{a} and @var{b}; that is
@code{@var{a} + @var{b}}.
@end deftypefn

@deftypefn {Runtime Function} int __mulvsi3 (int @var{a}, int @var{b})
@deftypefnx {Runtime Function} long __mulvdi3 (long @var{a}, long @var{b})
The functions return the product of @var{a} and @var{b}; that is
@code{@var{a} * @var{b}}.
@end deftypefn

@deftypefn {Runtime Function} int __negvsi2 (int @var{a})
@deftypefnx {Runtime Function} long __negvdi2 (long @var{a})
These functions return the negation of @var{a}; that is @code{-@var{a}}.
@end deftypefn

@deftypefn {Runtime Function} int __subvsi3 (int @var{a}, int @var{b})
@deftypefnx {Runtime Function} long __subvdi3 (long @var{a}, long @var{b})
These functions return the difference between @var{b} and @var{a};
that is @code{@var{a} - @var{b}}.
@end deftypefn

@subsection Bit operations

@deftypefn {Runtime Function} int __clzsi2 (int @var{a})
@deftypefnx {Runtime Function} int __clzdi2 (long @var{a})
@deftypefnx {Runtime Function} int __clzti2 (long long @var{a})
These functions return the number of leading 0-bits in @var{a}, starting
at the most significant bit position.  If @var{a} is zero, the result is
undefined.
@end deftypefn

@deftypefn {Runtime Function} int __ctzsi2 (int @var{a})
@deftypefnx {Runtime Function} int __ctzdi2 (long @var{a})
@deftypefnx {Runtime Function} int __ctzti2 (long long @var{a})
These functions return the number of trailing 0-bits in @var{a}, starting
at the least significant bit position.  If @var{a} is zero, the result is
undefined.
@end deftypefn

@deftypefn {Runtime Function} int __ffsdi2 (long @var{a})
@deftypefnx {Runtime Function} int __ffsti2 (long long @var{a})
These functions return the index of the least significant 1-bit in @var{a},
or the value zero if @var{a} is zero.  The least significant bit is index
one.
@end deftypefn

@deftypefn {Runtime Function} int __paritysi2 (int @var{a})
@deftypefnx {Runtime Function} int __paritydi2 (long @var{a})
@deftypefnx {Runtime Function} int __parityti2 (long long @var{a})
These functions return the value zero if the number of bits set in
@var{a} is even, and the value one otherwise.
@end deftypefn

@deftypefn {Runtime Function} int __popcountsi2 (int @var{a})
@deftypefnx {Runtime Function} int __popcountdi2 (long @var{a})
@deftypefnx {Runtime Function} int __popcountti2 (long long @var{a})
These functions return the number of bits set in @var{a}.
@end deftypefn

@node Soft float library routines
@section Routines for floating point emulation
@cindex soft float library
@cindex arithmetic library
@cindex math library
@opindex msoft-float

The software floating point library is used on machines which do not
have hardware support for floating point.  It is also used whenever
@option{-msoft-float} is used to disable generation of floating point
instructions.  (Not all targets support this switch.)

For compatibility with other compilers, the floating point emulation
routines can be renamed with the @code{DECLARE_LIBRARY_RENAMES} macro
(@pxref{Library Calls}).  In this section, the default names are used.

Presently the library does not support @code{XFmode}, which is used
for @code{long double} on some architectures.

@subsection Arithmetic functions

@deftypefn {Runtime Function} float __addsf3 (float @var{a}, float @var{b})
@deftypefnx {Runtime Function} double __adddf3 (double @var{a}, double @var{b})
@deftypefnx {Runtime Function} {long double} __addtf3 (long double @var{a}, long double @var{b})
@deftypefnx {Runtime Function} {long double} __addxf3 (long double @var{a}, long double @var{b})
These functions return the sum of @var{a} and @var{b}.
@end deftypefn

@deftypefn {Runtime Function} float __subsf3 (float @var{a}, float @var{b})
@deftypefnx {Runtime Function} double __subdf3 (double @var{a}, double @var{b})
@deftypefnx {Runtime Function} {long double} __subtf3 (long double @var{a}, long double @var{b})
@deftypefnx {Runtime Function} {long double} __subxf3 (long double @var{a}, long double @var{b})
These functions return the difference between @var{b} and @var{a};
that is, @w{@math{@var{a} - @var{b}}}.
@end deftypefn

@deftypefn {Runtime Function} float __mulsf3 (float @var{a}, float @var{b})
@deftypefnx {Runtime Function} double __muldf3 (double @var{a}, double @var{b})
@deftypefnx {Runtime Function} {long double} __multf3 (long double @var{a}, long double @var{b})
@deftypefnx {Runtime Function} {long double} __mulxf3 (long double @var{a}, long double @var{b})
These functions return the product of @var{a} and @var{b}.
@end deftypefn

@deftypefn {Runtime Function} float __divsf3 (float @var{a}, float @var{b})
@deftypefnx {Runtime Function} double __divdf3 (double @var{a}, double @var{b})
@deftypefnx {Runtime Function} {long double} __divtf3 (long double @var{a}, long double @var{b})
@deftypefnx {Runtime Function} {long double} __divxf3 (long double @var{a}, long double @var{b})
These functions return the quotient of @var{a} and @var{b}; that is,
@w{@math{@var{a} / @var{b}}}.
@end deftypefn

@deftypefn {Runtime Function} float __negsf2 (float @var{a})
@deftypefnx {Runtime Function} double __negdf2 (double @var{a})
@deftypefnx {Runtime Function} {long double} __negtf2 (long double @var{a})
@deftypefnx {Runtime Function} {long double} __negxf2 (long double @var{a})
These functions return the negation of @var{a}.  They simply flip the
sign bit, so they can produce negative zero and negative NaN.
@end deftypefn

@subsection Conversion functions

@deftypefn {Runtime Function} double __extendsfdf2 (float @var{a})
@deftypefnx {Runtime Function} {long double} __extendsftf2 (float @var{a})
@deftypefnx {Runtime Function} {long double} __extendsfxf2 (float @var{a})
@deftypefnx {Runtime Function} {long double} __extenddftf2 (double @var{a})
@deftypefnx {Runtime Function} {long double} __extenddfxf2 (double @var{a})
These functions extend @var{a} to the wider mode of their return
type.
@end deftypefn

@deftypefn {Runtime Function} double __truncxfdf2 (long double @var{a})
@deftypefnx {Runtime Function} double __trunctfdf2 (long double @var{a})
@deftypefnx {Runtime Function} float __truncxfsf2 (long double @var{a})
@deftypefnx {Runtime Function} float __trunctfsf2 (long double @var{a})
@deftypefnx {Runtime Function} float __truncdfsf2 (double @var{a})
These functions truncate @var{a} to the narrower mode of their return
type, rounding toward zero.
@end deftypefn

@deftypefn {Runtime Function} int __fixsfsi (float @var{a})
@deftypefnx {Runtime Function} int __fixdfsi (double @var{a})
@deftypefnx {Runtime Function} int __fixtfsi (long double @var{a})
@deftypefnx {Runtime Function} int __fixxfsi (long double @var{a})
These functions convert @var{a} to a signed integer, rounding toward zero.
@end deftypefn

@deftypefn {Runtime Function} long __fixsfdi (float @var{a})
@deftypefnx {Runtime Function} long __fixdfdi (double @var{a})
@deftypefnx {Runtime Function} long __fixtfdi (long double @var{a})
@deftypefnx {Runtime Function} long __fixxfdi (long double @var{a})
These functions convert @var{a} to a signed long, rounding toward zero.
@end deftypefn

@deftypefn {Runtime Function} {long long} __fixsfti (float @var{a})
@deftypefnx {Runtime Function} {long long} __fixdfti (double @var{a})
@deftypefnx {Runtime Function} {long long} __fixtfti (long double @var{a})
@deftypefnx {Runtime Function} {long long} __fixxfti (long double @var{a})
These functions convert @var{a} to a signed long long, rounding toward zero.
@end deftypefn

@deftypefn {Runtime Function} {unsigned int} __fixunssfsi (float @var{a})
@deftypefnx {Runtime Function} {unsigned int} __fixunsdfsi (double @var{a})
@deftypefnx {Runtime Function} {unsigned int} __fixunstfsi (long double @var{a})
@deftypefnx {Runtime Function} {unsigned int} __fixunsxfsi (long double @var{a})
These functions convert @var{a} to an unsigned integer, rounding
toward zero.  Negative values all become zero.
@end deftypefn

@deftypefn {Runtime Function} {unsigned long} __fixunssfdi (float @var{a})
@deftypefnx {Runtime Function} {unsigned long} __fixunsdfdi (double @var{a})
@deftypefnx {Runtime Function} {unsigned long} __fixunstfdi (long double @var{a})
@deftypefnx {Runtime Function} {unsigned long} __fixunsxfdi (long double @var{a})
These functions convert @var{a} to an unsigned long, rounding
toward zero.  Negative values all become zero.
@end deftypefn

@deftypefn {Runtime Function} {unsigned long long} __fixunssfti (float @var{a})
@deftypefnx {Runtime Function} {unsigned long long} __fixunsdfti (double @var{a})
@deftypefnx {Runtime Function} {unsigned long long} __fixunstfti (long double @var{a})
@deftypefnx {Runtime Function} {unsigned long long} __fixunsxfti (long double @var{a})
These functions convert @var{a} to an unsigned long long, rounding
toward zero.  Negative values all become zero.
@end deftypefn

@deftypefn {Runtime Function} float __floatsisf (int @var{i})
@deftypefnx {Runtime Function} double __floatsidf (int @var{i})
@deftypefnx {Runtime Function} {long double} __floatsitf (int @var{i})
@deftypefnx {Runtime Function} {long double} __floatsixf (int @var{i})
These functions convert @var{i}, a signed integer, to floating point.
@end deftypefn

@deftypefn {Runtime Function} float __floatdisf (long @var{i})
@deftypefnx {Runtime Function} double __floatdidf (long @var{i})
@deftypefnx {Runtime Function} {long double} __floatditf (long @var{i})
@deftypefnx {Runtime Function} {long double} __floatdixf (long @var{i})
These functions convert @var{i}, a signed long, to floating point.
@end deftypefn

@deftypefn {Runtime Function} float __floattisf (long long @var{i})
@deftypefnx {Runtime Function} double __floattidf (long long @var{i})
@deftypefnx {Runtime Function} {long double} __floattitf (long long @var{i})
@deftypefnx {Runtime Function} {long double} __floattixf (long long @var{i})
These functions convert @var{i}, a signed long long, to floating point.
@end deftypefn

@subsection Comparison functions

There are two sets of basic comparison functions.

@deftypefn {Runtime Function} int __cmpsf2 (float @var{a}, float @var{b})
@deftypefnx {Runtime Function} int __cmpdf2 (double @var{a}, double @var{b})
@deftypefnx {Runtime Function} int __cmptf2 (long double @var{a}, long double @var{b})
These functions calculate @math{a <=> b}.  That is, if @var{a} is less
than @var{b}, they return -1; if @var{a} is greater than @var{b}, they
return 1; and if @var{a} and @var{b} are equal they return 0.  If
either argument is NaN they return 1, but you should not rely on this;
if NaN is a possibility, use one of the higher-level comparison
functions.
@end deftypefn

@deftypefn {Runtime Function} int __unordsf2 (float @var{a}, float @var{b})
@deftypefnx {Runtime Function} int __unorddf2 (double @var{a}, double @var{b})
@deftypefnx {Runtime Function} int __unordtf2 (long double @var{a}, long double @var{b})
These functions return a nonzero value if either argument is NaN, otherwise 0.
@end deftypefn

There is also a complete group of higher level functions which
correspond directly to comparison operators.  They implement the ISO C
semantics for floating-point comparisons, taking NaN into account.
Pay careful attention to the return values defined for each set.
Under the hood, all of these routines are implemented as

@smallexample
  if (__unord@var{X}f2 (a, b))
    return @var{E};
  return __cmp@var{X}f2 (a, b);
@end smallexample

@noindent
where @var{E} is a constant chosen to give the proper behavior for
NaN.  Thus, the meaning of the return value is different for each set.
Do not rely on this implementation; only the semantics documented
below are guaranteed.

@deftypefn {Runtime Function} int __eqsf2 (float @var{a}, float @var{b})
@deftypefnx {Runtime Function} int __eqdf2 (double @var{a}, double @var{b})
@deftypefnx {Runtime Function} int __eqtf2 (long double @var{a}, long double @var{b})
These functions return zero if neither argument is NaN, and @var{a} and
@var{b} are equal.
@end deftypefn

@deftypefn {Runtime Function} int __nesf2 (float @var{a}, float @var{b})
@deftypefnx {Runtime Function} int __nedf2 (double @var{a}, double @var{b})
@deftypefnx {Runtime Function} int __netf2 (long double @var{a}, long double @var{b})
These functions return a nonzero value if either argument is NaN, or
if @var{a} and @var{b} are unequal.
@end deftypefn

@deftypefn {Runtime Function} int __gesf2 (float @var{a}, float @var{b})
@deftypefnx {Runtime Function} int __gedf2 (double @var{a}, double @var{b})
@deftypefnx {Runtime Function} int __getf2 (long double @var{a}, long double @var{b})
These functions return a value greater than or equal to zero if
neither argument is NaN, and @var{a} is greater than or equal to
@var{b}.
@end deftypefn

@deftypefn {Runtime Function} int __ltsf2 (float @var{a}, float @var{b})
@deftypefnx {Runtime Function} int __ltdf2 (double @var{a}, double @var{b})
@deftypefnx {Runtime Function} int __lttf2 (long double @var{a}, long double @var{b})
These functions return a value less than zero if neither argument is
NaN, and @var{a} is strictly less than @var{b}.
@end deftypefn

@deftypefn {Runtime Function} int __lesf2 (float @var{a}, float @var{b})
@deftypefnx {Runtime Function} int __ledf2 (double @var{a}, double @var{b})
@deftypefnx {Runtime Function} int __letf2 (long double @var{a}, long double @var{b})
These functions return a value less than or equal to zero if neither
argument is NaN, and @var{a} is less than or equal to @var{b}.
@end deftypefn

@deftypefn {Runtime Function} int __gtsf2 (float @var{a}, float @var{b})
@deftypefnx {Runtime Function} int __gtdf2 (double @var{a}, double @var{b})
@deftypefnx {Runtime Function} int __gttf2 (long double @var{a}, long double @var{b})
These functions return a value greater than zero if neither argument
is NaN, and @var{a} is strictly greater than @var{b}.
@end deftypefn

@node Exception handling routines
@section Language-independent routines for exception handling

document me!

@smallexample
  _Unwind_DeleteException
  _Unwind_Find_FDE
  _Unwind_ForcedUnwind
  _Unwind_GetGR
  _Unwind_GetIP
  _Unwind_GetLanguageSpecificData
  _Unwind_GetRegionStart
  _Unwind_GetTextRelBase
  _Unwind_GetDataRelBase
  _Unwind_RaiseException
  _Unwind_Resume
  _Unwind_SetGR
  _Unwind_SetIP
  _Unwind_FindEnclosingFunction
  _Unwind_SjLj_Register
  _Unwind_SjLj_Unregister
  _Unwind_SjLj_RaiseException
  _Unwind_SjLj_ForcedUnwind
  _Unwind_SjLj_Resume
  __deregister_frame
  __deregister_frame_info
  __deregister_frame_info_bases
  __register_frame
  __register_frame_info
  __register_frame_info_bases
  __register_frame_info_table
  __register_frame_info_table_bases
  __register_frame_table
@end smallexample

@node Miscellaneous routines
@section Miscellaneous runtime library routines

@subsection Cache control functions
@deftypefn {Runtime Function} void __clear_cache (char *@var{beg}, char *@var{end})
This function clears the instruction cache between @var{beg} and @var{end}.
@end deftypefn