[PATCH v2 2/4] riscv: Add Zfa implementations for fmaximum and fminimum

[Julian Zhu]

Use the Zfa fmaxm and fminm instructions for the NaN-propagating C23
maximum and minimum operations in float and double precision, which they
implement directly: one instruction and no branch, against the eight
instructions and a branch the generic implementation needs even with Zfa
in -march.

Signed-off-by: Julian Zhu <jz531210@gmail.com>
---
 sysdeps/riscv/rvd/s_fmaximum.c  | 44 +++++++++++++++++++++++++++++++++
 sysdeps/riscv/rvd/s_fminimum.c  | 42 +++++++++++++++++++++++++++++++
 sysdeps/riscv/rvf/s_fmaximumf.c | 42 +++++++++++++++++++++++++++++++
 sysdeps/riscv/rvf/s_fminimumf.c | 42 +++++++++++++++++++++++++++++++
 4 files changed, 170 insertions(+)
 create mode 100644 sysdeps/riscv/rvd/s_fmaximum.c
 create mode 100644 sysdeps/riscv/rvd/s_fminimum.c
 create mode 100644 sysdeps/riscv/rvf/s_fmaximumf.c
 create mode 100644 sysdeps/riscv/rvf/s_fminimumf.c

diff --git a/sysdeps/riscv/rvd/s_fmaximum.c b/sysdeps/riscv/rvd/s_fmaximum.c
new file mode 100644
index 0000000000..39b0f4658f
--- /dev/null
+++ b/sysdeps/riscv/rvd/s_fmaximum.c
@@ -0,0 +1,44 @@
+/* fmaximum().  RISC-V version.
+   Copyright (C) 2026 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/>.  */
+
+/* fmaximum is the IEEE 754-2019 maximum operation: like fmaximum_num but
+   NaN-propagating, so a NaN operand yields a quiet NaN result, and a
+   signaling NaN also raises the invalid exception.  Zfa's fmaxm.d
+   implements it in a single instruction; without Zfa no instruction
+   implements it, so use the generic implementation.  */
+
+#ifdef __riscv_zfa
+
+# include <math.h>
+# include <libm-alias-double.h>
+
+double
+__fmaximum (double x, double y)
+{
+  double res;
+  asm ("fmaxm.d %0, %1, %2" : "=f" (res) : "f" (x), "f" (y));
+  return res;
+}
+libm_alias_double (__fmaximum, fmaximum)
+
+#else
+
+# include <math-type-macros-double.h>
+# include <s_fmaximum_template.c>
+
+#endif
diff --git a/sysdeps/riscv/rvd/s_fminimum.c b/sysdeps/riscv/rvd/s_fminimum.c
new file mode 100644
index 0000000000..7726269a55
--- /dev/null
+++ b/sysdeps/riscv/rvd/s_fminimum.c
@@ -0,0 +1,42 @@
+/* fminimum().  RISC-V version.
+   Copyright (C) 2026 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/>.  */
+
+/* See s_fmaximum.c for a description of the semantics and of why the
+   fast path is gated on Zfa; fminm.d implements minimum for double
+   precision.  */
+
+#ifdef __riscv_zfa
+
+# include <math.h>
+# include <libm-alias-double.h>
+
+double
+__fminimum (double x, double y)
+{
+  double res;
+  asm ("fminm.d %0, %1, %2" : "=f" (res) : "f" (x), "f" (y));
+  return res;
+}
+libm_alias_double (__fminimum, fminimum)
+
+#else
+
+# include <math-type-macros-double.h>
+# include <s_fminimum_template.c>
+
+#endif
diff --git a/sysdeps/riscv/rvf/s_fmaximumf.c b/sysdeps/riscv/rvf/s_fmaximumf.c
new file mode 100644
index 0000000000..4b30a5457f
--- /dev/null
+++ b/sysdeps/riscv/rvf/s_fmaximumf.c
@@ -0,0 +1,42 @@
+/* fmaximumf().  RISC-V version.
+   Copyright (C) 2026 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/>.  */
+
+/* See s_fmaximum.c for a description of the semantics and of why the
+   fast path is gated on Zfa; fmaxm.s implements maximum for single
+   precision.  */
+
+#ifdef __riscv_zfa
+
+# include <math.h>
+# include <libm-alias-float.h>
+
+float
+__fmaximumf (float x, float y)
+{
+  float res;
+  asm ("fmaxm.s %0, %1, %2" : "=f" (res) : "f" (x), "f" (y));
+  return res;
+}
+libm_alias_float (__fmaximum, fmaximum)
+
+#else
+
+# include <math-type-macros-float.h>
+# include <s_fmaximum_template.c>
+
+#endif
diff --git a/sysdeps/riscv/rvf/s_fminimumf.c b/sysdeps/riscv/rvf/s_fminimumf.c
new file mode 100644
index 0000000000..3faba4b91f
--- /dev/null
+++ b/sysdeps/riscv/rvf/s_fminimumf.c
@@ -0,0 +1,42 @@
+/* fminimumf().  RISC-V version.
+   Copyright (C) 2026 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/>.  */
+
+/* See s_fmaximum.c for a description of the semantics and of why the
+   fast path is gated on Zfa; fminm.s implements minimum for single
+   precision.  */
+
+#ifdef __riscv_zfa
+
+# include <math.h>
+# include <libm-alias-float.h>
+
+float
+__fminimumf (float x, float y)
+{
+  float res;
+  asm ("fminm.s %0, %1, %2" : "=f" (res) : "f" (x), "f" (y));
+  return res;
+}
+libm_alias_float (__fminimum, fminimum)
+
+#else
+
+# include <math-type-macros-float.h>
+# include <s_fminimum_template.c>
+
+#endif
-- 
2.53.0