Add trivial assembler implementations of sqrt()/sqrtf().

10x faster in the usual bionic benchmarks.

Test: treehugger
Change-Id: If121cb1ed1ff0756310f34cbaa2c14e28484f1b8

libm/Android.bp

@@ -347,6 +347,12 @@ cc_library {
         riscv64: {
             srcs: [
                 "riscv64/fenv.c",
+                "riscv64/sqrt.S",
+            ],
+
+            exclude_srcs: [
+                "upstream-freebsd/lib/msun/src/e_sqrt.c",
+                "upstream-freebsd/lib/msun/src/e_sqrtf.c",
             ],
             version_script: ":libm.riscv64.map",
         },

libm/riscv64/sqrt.S

@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <private/bionic_asm.h>
+
+ENTRY(sqrt)
+  fsqrt.d fa0, fa0
+  ret
+END(sqrt)
+
+ENTRY(sqrtf)
+  fsqrt.s fa0, fa0
+  ret
+END(sqrtf)