math: Optimize float ilogb/llogb

It removes the wrapper by moving the error/EDOM handling to an
out-of-line implementation (__math_invalidf_i/__math_invalidf_li).
Also, __glibc_unlikely is used on errors case since it helps
code generation on recent gcc.

The code now builds to with gcc-14 on aarch64:

0000000000000000 <__ilogbf>:
   0:   1e260000        fmov    w0, s0
   4:   d3577801        ubfx    x1, x0, #23, #8
   8:   340000e1        cbz     w1, 24 <__ilogbf+0x24>
   c:   5101fc20        sub     w0, w1, #0x7f
  10:   7103fc3f        cmp     w1, #0xff
  14:   54000040        b.eq    1c <__ilogbf+0x1c>  // b.none
  18:   d65f03c0        ret
  1c:   12b00000        mov     w0, #0x7fffffff                 // #2147483647
  20:   14000000        b       0 <__math_invalidf_i>
  24:   53175800        lsl     w0, w0, #9
  28:   340000a0        cbz     w0, 3c <__ilogbf+0x3c>
  2c:   5ac01000        clz     w0, w0
  30:   12800fc1        mov     w1, #0xffffff81                 // #-127
  34:   4b000020        sub     w0, w1, w0
  38:   d65f03c0        ret
  3c:   320107e0        mov     w0, #0x80000001                 // #-2147483647
  40:   14000000        b       0 <__math_invalidf_i>

Some ABI requires additional adjustments:

  * i386 and m68k requires to use the template version, since
    both provide __ieee754_ilogb implementatations.

  * loongarch uses a custom implementation as well.

  * powerpc64le also has a custom implementation for POWER9, which
    is also used for float and float128 version.  The generic
    e_ilogb.c implementation is moved on powerpc to keep the
    current code as-is.

Checked on aarch64-linux-gnu and x86_64-linux-gnu.

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>
This commit is contained in:
Adhemerval Zanella 2025-04-21 13:45:31 -03:00
parent afe09d44f3
commit 39775f00b1
15 changed files with 220 additions and 80 deletions

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@ -0,0 +1,2 @@
#include <math-type-macros-float.h>
#include <w_ilogb_template.c>

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@ -0,0 +1,2 @@
#include <math-type-macros-float.h>
#include <w_llogb_template.c>

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@ -1,41 +1 @@
/* Get integer exponent of a floating-point value.
Copyright (C) 1999-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <limits.h>
#include <math.h>
#include <stdbit.h>
#include "math_config.h"
int
__ieee754_ilogbf (float x)
{
uint32_t ux = asuint (x);
int ex = (ux & ~SIGN_MASK) >> MANTISSA_WIDTH;
if (ex == 0) /* zero or subnormal */
{
/* Clear sign and exponent. */
ux <<= 1 + EXPONENT_WIDTH;
if (ux == 0)
return FP_ILOGB0;
/* subnormal */
return -127 - stdc_leading_zeros (ux);
}
if (ex == EXPONENT_MASK >> MANTISSA_WIDTH) /* NaN or Inf */
return ux << (1 + EXPONENT_WIDTH) ? FP_ILOGBNAN : INT_MAX;
return ex - 127;
}
/* ilogbf is implemented at w_ilogbf.c */

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@ -208,6 +208,8 @@ attribute_hidden float __math_uflowf (uint32_t);
attribute_hidden float __math_may_uflowf (uint32_t);
attribute_hidden float __math_divzerof (uint32_t);
attribute_hidden float __math_invalidf (float);
attribute_hidden int __math_invalidf_i (int);
attribute_hidden long int __math_invalidf_li (long int);
attribute_hidden float __math_edomf (float x);
/* Shared between expf, exp2f, exp10f, and powf. */

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@ -16,6 +16,7 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <math-barriers.h>
#include "math_config.h"
#if WANT_ERRNO
@ -27,8 +28,24 @@ with_errnof (float y, int e)
errno = e;
return y;
}
NOINLINE static int
with_errnof_i (int y, int e)
{
errno = e;
return y;
}
NOINLINE static long int
with_errnof_li (long int y, int e)
{
errno = e;
return y;
}
#else
# define with_errnof(x, e) (x)
# define with_errnof_i(x, x) (x)
# define with_errnof_li(x, x) (x)
#endif
attribute_hidden float
@ -80,3 +97,19 @@ __math_invalidf (float x)
float y = (x - x) / (x - x);
return isnan (x) ? y : with_errnof (y, EDOM);
}
attribute_hidden int
__math_invalidf_i (int x)
{
float y = 0.0f / 0.0f;
math_force_eval (y);
return with_errnof_i (x, EDOM);
}
attribute_hidden long int
__math_invalidf_li (long int x)
{
float y = 0.0f / 0.0f;
math_force_eval (y);
return with_errnof_li (x, EDOM);
}

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@ -0,0 +1,38 @@
/* Get integer exponent of a floating-point value.
Copyright (C) 1999-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
static inline RET_TYPE
IMPL_NAME (float x)
{
uint32_t ux = asuint (x);
int ex = (ux & ~SIGN_MASK) >> MANTISSA_WIDTH;
if (__glibc_unlikely (ex == 0))
{
/* Zero or subnormal.
Clear sign and exponent. */
ux <<= 1 + EXPONENT_WIDTH;
if (ux == 0)
return RET_INVALID (RET_LOGB0);
/* subnormal */
return (RET_TYPE)-127 - stdc_leading_zeros (ux);
}
if (__glibc_unlikely (ex == EXPONENT_MASK >> MANTISSA_WIDTH))
/* NaN or Inf */
return RET_INVALID (ux << (1 + EXPONENT_WIDTH) ? RET_LOGBNAN : RET_LOGMAX);
return ex - 127;
}

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@ -0,0 +1,53 @@
/* Get integer exponent of a floating-point value.
Copyright (C) 1999-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <limits.h>
#include <math.h>
#include <stdbit.h>
#include <libm-alias-float.h>
#include <math-type-macros-float.h>
#include "math_config.h"
#ifdef DEF_AS_LLOGBF
# define DECL_NAME __llogb
# define FUNC_NAME llogb
# define RET_TYPE long int
# define RET_LOGB0 FP_LLOGB0
# define RET_LOGBNAN FP_LLOGBNAN
# define RET_LOGMAX LONG_MAX
# define RET_INVALID __math_invalidf_li
#else
# define DECL_NAME __ilogb
# define FUNC_NAME ilogb
# define RET_TYPE int
# define RET_LOGB0 FP_ILOGB0
# define RET_LOGBNAN FP_ILOGBNAN
# define RET_LOGMAX INT_MAX
# define RET_INVALID __math_invalidf_i
#endif
#define __IMPL_NAME(x,y) x ## _ ## y
#define _IMPL_NAME(x,y) __IMPL_NAME(x,y)
#define IMPL_NAME _IMPL_NAME(FUNC_NAME, impl)
#include <w_ilogbf-impl.h>
RET_TYPE
M_DECL_FUNC (DECL_NAME) (float x)
{
return IMPL_NAME (x);
}
libm_alias_float (DECL_NAME, FUNC_NAME);

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@ -0,0 +1,2 @@
#define DEF_AS_LLOGBF
#include "w_ilogbf.c"

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@ -1,39 +1 @@
/* __ieee754_ilogbf(). LoongArch version.
Copyright (C) 2022-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#define NO_MATH_REDIRECT
#include <math.h>
#include <fpu_control.h>
int
__ieee754_ilogbf (float x)
{
int x_cond;
asm volatile ("fclass.s \t%0, %1" : "=f" (x_cond) : "f" (x));
if (__glibc_unlikely (x_cond & _FCLASS_ZERO))
return FP_ILOGB0;
else if (__glibc_unlikely (x_cond & ( _FCLASS_NAN | _FCLASS_INF)))
return FP_ILOGBNAN;
else
{
asm volatile ("fabs.s \t%0, %1" : "=f" (x) : "f" (x));
asm volatile ("flogb.s \t%0, %1" : "=f" (x) : "f" (x));
return x;
}
}
/* ilogbf is implemented at w_ilogbf.c */

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@ -0,0 +1,37 @@
/* Get integer exponent of a floating-point value. LoongArch version.
Copyright (C) 2022-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <fpu_control.h>
static inline RET_TYPE
IMPL_NAME (float x)
{
int x_cond;
asm volatile ("fclass.s \t%0, %1" : "=f" (x_cond) : "f" (x));
if (__glibc_unlikely (x_cond & _FCLASS_ZERO))
return RET_INVALID (RET_LOGB0);
else if (__glibc_unlikely (x_cond & ( _FCLASS_NAN | _FCLASS_INF)))
return RET_INVALID (RET_LOGBNAN);
else
{
asm volatile ("fabs.s \t%0, %1" : "=f" (x) : "f" (x));
asm volatile ("flogb.s \t%0, %1" : "=f" (x) : "f" (x));
return x;
}
}

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@ -0,0 +1,2 @@
#include <math-type-macros-float.h>
#include <w_ilogb_template.c>

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@ -0,0 +1,2 @@
#include <math-type-macros-float.h>
#include <w_llogb_template.c>

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@ -0,0 +1,41 @@
/* Get integer exponent of a floating-point value.
Copyright (C) 1999-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <limits.h>
#include <math.h>
#include <stdbit.h>
#include "sysdeps/ieee754/flt-32/math_config.h"
int
__ieee754_ilogbf (float x)
{
uint32_t ux = asuint (x);
int ex = (ux & ~SIGN_MASK) >> MANTISSA_WIDTH;
if (ex == 0) /* zero or subnormal */
{
/* Clear sign and exponent. */
ux <<= 1 + EXPONENT_WIDTH;
if (ux == 0)
return FP_ILOGB0;
/* sbunormal */
return -127 - stdc_leading_zeros (ux);
}
if (ex == EXPONENT_MASK >> MANTISSA_WIDTH) /* NaN or Inf */
return ux << (1 + EXPONENT_WIDTH) ? FP_ILOGBNAN : INT_MAX;
return ex - 127;
}

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@ -0,0 +1,2 @@
#include <math-type-macros-float.h>
#include <w_ilogb_template.c>

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@ -0,0 +1,2 @@
#include <math-type-macros-float.h>
#include <w_llogb_template.c>