riscv-rv32i: Add sqrtf function

The int_sqrtf() requires this function if we enable FPU.

BRANCH=none
BUG=none
TEST=manual testing on console command:
sqrtf(1.23) = 1.10
sqrtf(0.45) = 0.67
sqrtf(0) = 0

Change-Id: I354453674559ff2e1b956c9dba47baa493332871
Signed-off-by: Dino Li <dino.li@ite.com.tw>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1982298
Reviewed-by: Jett Rink <jettrink@chromium.org>
Commit-Queue: Dino Li <Dino.Li@ite.com.tw>
Tested-by: Dino Li <Dino.Li@ite.com.tw>

core/riscv-rv32i/build.mk

@@ -14,4 +14,4 @@ $(call set-option,CROSS_COMPILE,$(CROSS_COMPILE_riscv),\
 CFLAGS_CPU+=-march=rv32imafc -mabi=ilp32f -Os
 LDFLAGS_EXTRA+=-mrelax
 
-core-y=cpu.o init.o panic.o task.o switch.o __builtin.o
+core-y=cpu.o init.o panic.o task.o switch.o __builtin.o math.o

core/riscv-rv32i/include/math.h

@@ -0,0 +1,13 @@
+/* Copyright 2020 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* Math utility functions for RISC-V */
+
+#ifndef __CROS_EC_MATH_H
+#define __CROS_EC_MATH_H
+
+float sqrtf(float x);
+
+#endif  /* __CROS_EC_MATH_H */

core/riscv-rv32i/math.c

@@ -0,0 +1,19 @@
+/* Copyright 2020 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "common.h"
+
+#ifdef CONFIG_FPU
+/* Single precision floating point square root. */
+float sqrtf(float x)
+{
+	asm volatile (
+		"fsqrt.s %0, %1"
+		: "=f" (x)
+		: "f" (x));
+
+	return x;
+}
+#endif