On Mon, Aug 21, 2023 at 05:32:04PM +0000, Joseph Myers wrote:
> I think the libgcc functions (i.e. those exported by libgcc, to which
> references are generated by the compiler) need documenting in libgcc.texi.
> Internal functions or macros in the libgcc patch need appropriate comments
> specifying their semantics; especially FP_TO_BITINT and FP_FROM_BITINT
> which have a lot of arguments and no comments saying what the semantics of
> the macros and their arguments are supposed to me.
Here is an incremental patch which does that.
2023-08-22 Jakub Jelinek <ja...@redhat.com>
PR c/102989
gcc/
* doc/libgcc.texi (Bit-precise integer arithmetic functions):
Document general rules for _BitInt support library functions
and document __mulbitint3 and __divmodbitint4.
(Conversion functions): Document __fix{s,d,x,t}fbitint,
__floatbitint{s,d,x,t,h,b}f, __bid_fix{s,d,t}dbitint and
__bid_floatbitint{s,d,t}d.
libgcc/
* libgcc2.c (bitint_negate): Add function comment.
* soft-fp/bitint.h (bitint_negate): Add function comment.
(FP_TO_BITINT, FP_FROM_BITINT): Add comment explaining the macros.
--- gcc/doc/libgcc.texi.jj 2023-01-16 11:52:16.115733593 +0100
+++ gcc/doc/libgcc.texi 2023-08-22 12:35:08.561348126 +0200
@@ -218,6 +218,51 @@ These functions return the number of bit
These functions return the @var{a} byteswapped.
@end deftypefn
+@subsection Bit-precise integer arithmetic functions
+
+@code{_BitInt(@var{N})} library functions operate on arrays of limbs, where
+each limb has @code{__LIBGCC_BITINT_LIMB_WIDTH__} bits and the limbs are
+ordered according to @code{__LIBGCC_BITINT_ORDER__} ordering. The most
+significant limb if @var{N} is not divisible by
+@code{__LIBGCC_BITINT_LIMB_WIDTH__} contains padding bits which should be
+ignored on read (sign or zero extended), but extended on write. For the
+library functions, all bit-precise integers regardless of @var{N} are
+represented like that, even when the target ABI says that for some small
+@var{N} they should be represented differently in memory. A pointer
+to the array of limbs argument is always accompanied with a bit size
+argument. If that argument is positive, it is number of bits and the
+number is assumed to be zero-extended to infinite precision, if that
+argument is negative, it is negated number of bits above which all bits
+are assumed to be sign-extended to infinite precision. These number of bits
+arguments don't need to match actual @var{N} for the operation used in the
+source, they could be lowered because of sign or zero extensions on the
+input or because value-range optimization figures value will need certain
+lower number of bits. For big-endian ordering of limbs, when lowering
+the bit size argument the pointer argument needs to be adjusted as well.
+Negative bit size argument should be always smaller or equal to @code{-2},
+because @code{signed _BitInt(1)} is not valid.
+For output arguments, either the corresponding bit size argument should
+be always positive (for multiplication and division), or is negative when
+the output of conversion from floating-point value is signed and positive
+when unsigned. The arrays of limbs output arguments point to should not
+overlap any inputs, while input arrays of limbs can overlap.
+@code{UBILtype} below stands for unsigned integer type with
+@code{__LIBGCC_BITINT_LIMB_WIDTH__} bit precision.
+
+@deftypefn {Runtime Function} void __mulbitint3 (@code{UBILtype} *@var{ret},
int32_t @var{retprec}, const @code{UBILtype} *u, int32_t @var{uprec}, const
@code{UBILtype} *v, int32_t @var{vprec})
+This function multiplies bit-precise integer operands @var{u} and @var{v} and
stores
+result into @var{retprec} precision bit-precise integer result @var{ret}.
+@end deftypefn
+
+@deftypefn {Runtime Function} void __divmodbitint4 (@code{UBILtype} *@var{q},
int32_t @var{qprec}, @code{UBILtype} *@var{r}, int32_t @var{rprec}, const
@code{UBILtype} *u, int32_t @var{uprec}, const @code{UBILtype} *v, int32_t
@var{vprec})
+This function divides bit-precise integer operands @var{u} and @var{v} and
stores
+quotient into @var{qprec} precision bit-precise integer result @var{q}
+(unless @var{q} is @code{NULL} and @var{qprec} is 0, in that case quotient
+is not stored anywhere) and remainder into @var{rprec} precision bit-precise
+integer result @var{r} (similarly, unless @var{r} is @code{NULL} and
@var{rprec}
+is 0).
+@end deftypefn
+
@node Soft float library routines
@section Routines for floating point emulation
@cindex soft float library
@@ -384,6 +429,27 @@ These functions convert @var{i}, an unsi
These functions convert @var{i}, an unsigned long long, to floating point.
@end deftypefn
+@deftypefn {Runtime Function} void __fixsfbitint (@code{UBILtype} *@var{r},
int32_t @var{rprec}, float @var{a})
+@deftypefnx {Runtime Function} void __fixdfbitint (@code{UBILtype} *@var{r},
int32_t @var{rprec}, double @var{a})
+@deftypefnx {Runtime Function} void __fixxfbitint (@code{UBILtype} *@var{r},
int32_t @var{rprec}, __float80 @var{a})
+@deftypefnx {Runtime Function} void __fixtfbitint (@code{UBILtype} *@var{r},
int32_t @var{rprec}, _Float128 @var{a})
+These functions convert @var{a} to bit-precise integer @var{r}, rounding
toward zero.
+If @var{rprec} is positive, it converts to unsigned bit-precise integer and
+negative values all become zero, if @var{rprec} is negative, it converts
+to signed bit-precise integer.
+@end deftypefn
+
+@deftypefn {Runtime Function} float __floatbitintsf (@code{UBILtype} *@var{i},
int32_t @var{iprec})
+@deftypefnx {Runtime Function} double __floatbitintdf (@code{UBILtype}
*@var{i}, int32_t @var{iprec})
+@deftypefnx {Runtime Function} __float80 __floatbitintxf (@code{UBILtype}
*@var{i}, int32_t @var{iprec})
+@deftypefnx {Runtime Function} _Float128 __floatbitinttf (@code{UBILtype}
*@var{i}, int32_t @var{iprec})
+@deftypefnx {Runtime Function} _Float16 __floatbitinthf (@code{UBILtype}
*@var{i}, int32_t @var{iprec})
+@deftypefnx {Runtime Function} __bf16 __floatbitintbf (@code{UBILtype}
*@var{i}, int32_t @var{iprec})
+These functions convert bit-precise integer @var{i} to floating point. If
+@var{iprec} is positive, it is conversion from unsigned bit-precise integer,
+otherwise from signed bit-precise integer.
+@end deftypefn
+
@subsection Comparison functions
There are two sets of basic comparison functions.
@@ -707,6 +773,23 @@ These functions convert @var{i}, an unsi
These functions convert @var{i}, an unsigned long, to decimal floating point.
@end deftypefn
+@deftypefn {Runtime Function} void __bid_fixsdbitint (@code{UBILtype}
*@var{r}, int32_t @var{rprec}, _Decimal32 @var{a})
+@deftypefnx {Runtime Function} void __bid_fixddbitint (@code{UBILtype}
*@var{r}, int32_t @var{rprec}, _Decimal64 @var{a})
+@deftypefnx {Runtime Function} void __bid_fixtdbitint (@code{UBILtype}
*@var{r}, int32_t @var{rprec}, _Decimal128 @var{a})
+These functions convert @var{a} to bit-precise integer @var{r}, rounding
toward zero.
+If @var{rprec} is positive, it converts to unsigned bit-precise integer and
+negative values all become zero, if @var{rprec} is negative, it converts
+to signed bit-precise integer.
+@end deftypefn
+
+@deftypefn {Runtime Function} _Decimal32 __bid_floatbitintsd (@code{UBILtype}
*@var{i}, int32_t @var{iprec})
+@deftypefnx {Runtime Function} _Decimal64 __bid_floatbitintdd (@code{UBILtype}
*@var{i}, int32_t @var{iprec})
+@deftypefnx {Runtime Function} _Decimal128 __bid_floatbitinttd
(@code{UBILtype} *@var{i}, int32_t @var{iprec})
+These functions convert bit-precise integer @var{i} to decimal floating point.
If
+@var{iprec} is positive, it is conversion from unsigned bit-precise integer,
+otherwise from signed bit-precise integer.
+@end deftypefn
+
@subsection Comparison functions
@deftypefn {Runtime Function} int __dpd_unordsd2 (_Decimal32 @var{a},
_Decimal32 @var{b})
--- libgcc/libgcc2.c.jj 2023-08-22 11:21:31.549370982 +0200
+++ libgcc/libgcc2.c 2023-08-22 13:24:46.198998697 +0200
@@ -1640,6 +1640,8 @@ __mulbitint3 (UWtype *ret, SItype retpre
#endif
#ifdef L_divmodbitint4
+/* D = -S. */
+
static void
bitint_negate (UWtype *d, const UWtype *s, SItype n)
{
--- libgcc/soft-fp/bitint.h.jj 2023-08-22 11:21:31.583370543 +0200
+++ libgcc/soft-fp/bitint.h 2023-08-22 13:06:01.346092498 +0200
@@ -160,6 +160,9 @@ bitint_reduce_prec (const UBILtype **p,
# define BITINT_END(be, le) (le)
#endif
+/* Negate N limbs from S into D. D and S should point to
+ the least significant limb. */
+
static inline __attribute__((__always_inline__)) void
bitint_negate (UBILtype *d, const UBILtype *s, SItype n)
{
@@ -175,6 +178,19 @@ bitint_negate (UBILtype *d, const UBILty
while (--n);
}
+/* Common final part of __fix?fbitint conversion functions.
+ The A floating point value should have been converted using
+ soft-fp macros into RV, U##DI##type DI##_BITS precise normal
+ integral type and SHIFT, how many bits should that value be
+ shifted to the left. R is pointer to limbs array passed to the
+ function, RN number of limbs in it, ARPREC absolute value of
+ RPREC argument passed to it, RSIZE number of significant bits in RV.
+ RSIGNED is non-zero if the result is signed bit-precise integer,
+ otherwise zero. If OVF is true, instead of storing RV shifted left
+ by SHIFT bits and zero or sign extended store minimum or maximum
+ of the signed or unsigned bit-precise integer type depending on if
+ RV contains the minimum or maximum signed or unsigned value. */
+
#define FP_TO_BITINT(r, rn, arprec, shift, rv, rsize, rsigned, ovf, DI) \
if (ovf) \
{ \
@@ -232,6 +248,16 @@ bitint_negate (UBILtype *d, const UBILty
* sizeof (UBILtype)); \
}
+/* Common initial part of __floatbitint?f conversion functions.
+ I and IPREC are arguments passed to those functions, convert that
+ into a pair of DI##type IV integer and SHIFT, such that converting
+ IV to floating point and multiplicating that by pow (2, SHIFT)
+ gives the expected result. IV size needs to be chosen such that
+ it is large than number of bits in floating-point mantissa and
+ contains there even at least a two bits below the mantissa for
+ rounding purposes. If any of the SHIFT bits shifted out is non-zero,
+ the least significant bit should be non-zero. */
+
#define FP_FROM_BITINT(i, iprec, iv, shift, DI)
\
do \
{ \
Jakub
