riscv: Fix autotools definitions and comments

Signed-off-by: Cosmin Truta <ctruta@gmail.com>

configure

@@ -1593,6 +1593,11 @@ Optional Features:
                           no/off: disable the optimizations; yes/on: turn on
                           unconditionally. If not specified: determined by the
                           compiler.
+  --enable-riscv-rvv
+                          Enable RISC-V Vector optimizations: =no/off, yes/on:
+                          no/off: disable the optimizations; yes/on: turn on
+                          unconditionally. If not specified: determined by the
+                          compiler.
 
 Optional Packages:
   --with-PACKAGE[=ARG]    use PACKAGE [ARG=yes]
@@ -15561,6 +15566,61 @@ else
   PNG_LOONGARCH_LSX_FALSE=
 fi
 
+# RISC-V RVV
+# =============
+
+# Check whether --enable-riscv-rvv was given.
+if test ${enable_riscv_rvv+y}
+then :
+  enableval=$enable_riscv_rvv; case "$enableval" in
+      no|off)
+         # disable the default enabling on __RVV__ systems:
+
+printf "%s\n" "#define PNG_RISCV_RVV_OPT 0" >>confdefs.h
+
+         # Prevent inclusion of the assembler files below:
+         enable_riscv_rvv=no ;;
+      check)
+
+printf "%s\n" "#define PNG_RISCV_RVV_CHECK_SUPPORTED /**/" >>confdefs.h
+;;
+      api)
+
+printf "%s\n" "#define PNG_RISCV_RVV_API_SUPPORTED /**/" >>confdefs.h
+;;
+      yes|on)
+
+printf "%s\n" "#define PNG_RISCV_RVV_OPT 2" >>confdefs.h
+
+         { printf "%s\n" "$as_me:${as_lineno-$LINENO}: WARNING: --enable-riscv-rvv: please specify 'check' or 'api';
+            if you want the optimizations unconditionally,
+            pass '-march=rv64gv1p0' or '-march=rv64gcv1p0' to the compiler." >&5
+printf "%s\n" "$as_me: WARNING: --enable-riscv-rvv: please specify 'check' or 'api';
+            if you want the optimizations unconditionally,
+            pass '-march=rv64gv1p0' or '-march=rv64gcv1p0' to the compiler." >&2;};;
+      *)
+         as_fn_error $? "--enable-riscv-rvv=${enable_riscv_rvv}:
+                      invalid argument" "$LINENO" 5
+   esac
+fi
+
+
+# Add RISCV-specific files to all builds where $host_cpu is arm ('riscv64*') or
+# where RISCV optimizations were explicitly requested. (This allows a fallback
+# if a future host CPU does not match 'riscv64*'.)
+
+ if test "$enable_riscv_rvv" != 'no' &&
+    case "$host_cpu" in
+      riscv64) : ;;
+      *)    test "$enable_riscv_rvv" != '' ;;
+    esac; then
+  PNG_RISCV_RVV_TRUE=
+  PNG_RISCV_RVV_FALSE='#'
+else
+  PNG_RISCV_RVV_TRUE='#'
+  PNG_RISCV_RVV_FALSE=
+fi
+
 
 { printf "%s\n" "$as_me:${as_lineno-$LINENO}: Extra options for compiler: $PNG_COPTS" >&5
 printf "%s\n" "$as_me: Extra options for compiler: $PNG_COPTS" >&6;}
@@ -15784,6 +15844,10 @@ if test -z "${PNG_LOONGARCH_LSX_TRUE}" && test -z "${PNG_LOONGARCH_LSX_FALSE}";
   as_fn_error $? "conditional \"PNG_LOONGARCH_LSX\" was never defined.
 Usually this means the macro was only invoked conditionally." "$LINENO" 5
 fi
+if test -z "${PNG_RISCV_RVV_TRUE}" && test -z "${PNG_RISCV_RVV_FALSE}"; then
+  as_fn_error $? "conditional \"PNG_RISCV_RVV\" was never defined.
+Usually this means the macro was only invoked conditionally." "$LINENO" 5
+fi
 
 : "${CONFIG_STATUS=./config.status}"
 ac_write_fail=0

configure.ac

@@ -682,7 +682,7 @@ AS_HELP_STRING([[[--enable-riscv-rvv]]],
       [If not specified: determined by the compiler.]),
    [case "$enableval" in
       no|off)
-         # disable the default enabling on __ppc64__ systems:
+         # disable the default enabling on __riscv systems:
          AC_DEFINE([PNG_RISCV_RVV_OPT], [0],
                    [Disable RISC-V Vector optimizations])
          # Prevent inclusion of the platform-specific files below:

contrib/riscv-rvv/README

@@ -24,7 +24,7 @@ This is done in a 'configure' build by passing configure the argument:
 
    --enable-riscv-rvv=check
 
-Apart from the basic Linux implementation in contrib/riscv-vector/linux.c this
+Apart from the basic Linux implementation in contrib/riscv-rvv/linux.c this
 code is unsupported.  That means that it is not even compiled on a regular
 basis and may be broken in any given minor release.
 

png.h

@@ -3322,7 +3322,11 @@ PNG_EXPORT(245, int, png_image_write_to_memory, (png_imagep image, void *memory,
 #  define PNG_MIPS_MMI   12 /* HARDWARE: MIPS MMI SIMD instructions supported */
 #endif
 
-#define PNG_OPTION_NEXT  14 /* Next option - numbers must be even */
+#ifdef PNG_RISCV_RVV_API_SUPPORTED
+#  define PNG_RISCV_RVV   14 /* HARDWARE: RISC-V RVV SIMD instructions supported */
+#endif
+
+#define PNG_OPTION_NEXT  16 /* Next option - numbers must be even */
 
 /* Return values: NOTE: there are four values and 'off' is *not* zero */
 #define PNG_OPTION_UNSET   0 /* Unset - defaults to off */

pngpriv.h

@@ -145,29 +145,15 @@
 
 #ifndef PNG_RISCV_RVV_OPT
    /* RISCV_RVV optimizations are being controlled by the compiler settings,
-    * typically the target FPU then the compiler will define __RVV__ and we can rely
-    * unconditionally on NEON instructions not crashing, otherwise we must
-    * disable use of NEON instructions.
+    * typically the target compiler will define __riscv but the rvv extension
+    * availability has to be explicitly stated
     *
-    * NOTE: at present these optimizations depend on 'ALIGNED_MEMORY', so they
-    * can only be turned on automatically if that is supported too. If
-    * PNG_RISCV_RVV_OPT is set in CPPFLAGS (to >0) then riscv/riscv_init.c will fail
-    * to compile with an appropriate #error if ALIGNED_MEMORY has been turned
-    * off.
-    *
-    * Note that gcc and clang use the same __RVV__ flag. No known variations
-    * of this name is know as writing this code.
-    *
-    * To disable RISCV_RVV optimizations entirely, and skip compiling the
-    * associated assembler code, pass --enable-riscv-rvv=no to configure
-    * or put -DPNG_RISCV_RVV_OPT=0 in CPPFLAGS.
+    * To enable RISCV_RVV optimizations, and compile the
+    * associated code, pass --enable-riscv-rvv=yes or --enable-riscv-rvv=on
+    * to configure or put -DPNG_RISCV_RVV_OPT=2 in CPPFLAGS.
     */
-#  if defined(__RVV__) && defined(PNG_ALIGNED_MEMORY_SUPPORTED)
-#     define PNG_RISCV_RVV_OPT 2
-#  else
 #     define PNG_RISCV_RVV_OPT 0
 #endif
-#endif
 
 #if PNG_ARM_NEON_OPT > 0
    /* NEON optimizations are to be at least considered by libpng, so enable the

riscv/riscv_init.c

@@ -16,6 +16,10 @@
 
 #include <riscv_vector.h>
 
+#ifdef PNG_RISCV_RVV_CHECK_SUPPORTED
+#include <signal.h>
+#endif
+
 #ifdef PNG_RISCV_RVV_CHECK_SUPPORTED /* Do run-time checks */
 /* WARNING: it is strongly recommended that you do not build libpng with
  * run-time checks for CPU features if at all possible.  In the case of the
@@ -25,14 +29,14 @@
  *
  * You may set the macro PNG_RISCV_RVV_FILE to the file name of file containing
  * a fragment of C source code which defines the png_have_neon function.  There
- * are a number of implementations in contrib/riscv-vector, but the only one that
- * has partial support is contrib/riscv-vector/linux.c - a generic Linux
+ * are a number of implementations in contrib/riscv-rvv, but the only one that
+ * has partial support is contrib/riscv-rvv/linux.c - a generic Linux
  * implementation which reads /proc/cpuinfo.
  */
 
 #ifndef PNG_RISCV_RVV_FILE
 #  if defined(__linux__)
-#    define PNG_RISCV_RVV_FILE "contrib/riscv-vector/linux.c"
+#    define PNG_RISCV_RVV_FILE "contrib/riscv-rvv/linux.c"
 #  else
 #    error "No support for run-time RISC-V Vector checking; use compile-time options"
 #  endif