From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Fri, 23 Jan 2026 13:02:24 +0000 (-0300)
Subject: math: Optimize f{max,min}imum_mag{f,l,f128}
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8a7675663e03b73d6331f17f931762f8e2a33d2f;p=thirdparty%2Fglibc.git

math: Optimize f{max,min}imum_mag{f,l,f128}

Simplify order signal comparison and reorganize check to reduce
branches and allow targets to use conditional select/move.

With gcc-15 on aarch64 for fmaximum_mag:

* master:

0000000000000000 <__fmaximum_mag>:
   0:   d503245f        bti     c
   4:   1e60c004        fabs    d4, d0
   8:   1e60c023        fabs    d3, d1
   c:   1e632080        fcmp    d4, d3
  10:   5400008d        b.le    20 <__fmaximum_mag+0x20>
  14:   1e60401f        fmov    d31, d0
  18:   1e6043e0        fmov    d0, d31
  1c:   d65f03c0        ret
  20:   54000085        b.pl    30 <__fmaximum_mag+0x30>  // b.nfrst
  24:   1e60403f        fmov    d31, d1
  28:   1e6043e0        fmov    d0, d31
  2c:   d65f03c0        ret
  30:   54000161        b.ne    5c <__fmaximum_mag+0x5c>  // b.any
  34:   4f000402        movi    v2.4s, #0x0
  38:   1e6e101d        fmov    d29, #1.000000000000000000e+00
  3c:   6ee0f842        fneg    v2.2d, v2.2d
  40:   4ea21c5e        mov     v30.16b, v2.16b
  44:   2e7d1c22        bsl     v2.8b, v1.8b, v29.8b
  48:   2e7d1c1e        bsl     v30.8b, v0.8b, v29.8b
  4c:   1e6223d0        fcmpe   d30, d2
  50:   1e61ac1f        fcsel   d31, d0, d1, ge // ge = tcont
  54:   1e6043e0        fmov    d0, d31
  58:   d65f03c0        ret
  5c:   1e61281f        fadd    d31, d0, d1
  60:   1e6043e0        fmov    d0, d31
  64:   d65f03c0        ret

* patch:

0000000000000000 <__fmaximum_mag>:
   0:   d503245f        bti     c
   4:   1e612000        fcmp    d0, d1
   8:   540000e6        b.vs    24 <__fmaximum_mag+0x24>
   c:   1e60c01f        fabs    d31, d0
  10:   1e60c03e        fabs    d30, d1
  14:   1e7e23e0        fcmp    d31, d30
  18:   540000a0        b.eq    2c <__fmaximum_mag+0x2c>  // b.none
  1c:   1e60dc20        fcsel   d0, d1, d0, le
  20:   d65f03c0        ret
  24:   1e612800        fadd    d0, d0, d1
  28:   d65f03c0        ret
  2c:   9e660000        fmov    x0, d0
  30:   f100001f        cmp     x0, #0x0
  34:   1e60bc20        fcsel   d0, d1, d0, lt  // lt = tstop
  38:   d65f03c0        ret

Checked on x86_64-linux-gnu, aarch64-linux-gnu, i686-linux-gnu,
arm-linux-gnueabihf, powerpc64le-linux-gnu,
riscv64-linux-gnu-rv64imafdc-lp64d, and loongarch64-linux-gnuf64.

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>
---

diff --git a/math/s_fmaximum_mag_template.c b/math/s_fmaximum_mag_template.c
index 3f39599fcf..cff45a5ae7 100644
--- a/math/s_fmaximum_mag_template.c
+++ b/math/s_fmaximum_mag_template.c
@@ -21,14 +21,14 @@
 FLOAT
 M_DECL_FUNC (__fmaximum_mag) (FLOAT x, FLOAT y)
 {
-  FLOAT ax = M_FABS (x);
-  FLOAT ay = M_FABS (y);
-  if (isgreater (ax, ay))
-    return x;
-  else if (isless (ax, ay))
-    return y;
-  else if (ax == ay)
-    return (M_COPYSIGN (1, x) >= M_COPYSIGN (1, y) ? x : y);
+  if (__glibc_likely (!isunordered (x, y)))
+    {
+      FLOAT ax = M_FABS (x);
+      FLOAT ay = M_FABS (y);
+      if (__glibc_unlikely (ax == ay))
+        return signbit (x) ? y : x;
+      return isgreater (ax, ay) ? x : y;
+    }
   else
     return x + y;
 }
diff --git a/math/s_fminimum_mag_template.c b/math/s_fminimum_mag_template.c
index e67092d206..2858de8e46 100644
--- a/math/s_fminimum_mag_template.c
+++ b/math/s_fminimum_mag_template.c
@@ -21,14 +21,14 @@
 FLOAT
 M_DECL_FUNC (__fminimum_mag) (FLOAT x, FLOAT y)
 {
-  FLOAT ax = M_FABS (x);
-  FLOAT ay = M_FABS (y);
-  if (isless (ax, ay))
-    return x;
-  else if (isgreater (ax, ay))
-    return y;
-  else if (ax == ay)
-    return (M_COPYSIGN (1, x) <= M_COPYSIGN (1, y) ? x : y);
+  if (__glibc_likely (!isunordered (x, y)))
+    {
+      FLOAT ax = M_FABS (x);
+      FLOAT ay = M_FABS (y);
+      if (__glibc_unlikely (ax == ay))
+        return signbit (x) ? x : y;
+      return isless (ax, ay) ? x : y;
+    }
   else
     return x + y;
 }