[musl] [PATCH v4] math: add riscv64 round/roundf

[Meng Zhuo <mzh@mzh.io>]

---
v3 -> v4:
* add fabs(f) to avoild overflow.
* add comment on -0 copysign

Thanks for review!
How to implement "single cmp+branch on the bit representation of x"?
I've tried Google bit hacks of it. Could you give some tip or refs?
---
 src/math/riscv64/round.c  | 21 +++++++++++++++++++++
 src/math/riscv64/roundf.c | 21 +++++++++++++++++++++
 2 files changed, 42 insertions(+)
 create mode 100644 src/math/riscv64/round.c
 create mode 100644 src/math/riscv64/roundf.c

diff --git a/src/math/riscv64/round.c b/src/math/riscv64/round.c
new file mode 100644
index 00000000..7d7ade9d
--- /dev/null
+++ b/src/math/riscv64/round.c
@@ -0,0 +1,21 @@
+#include <math.h>
+
+#if __riscv_flen >= 64
+
+double round(double x)
+{
+	if (!isfinite(x) || fabs(x) >= 0x1p52) return x;
+	double tmp;
+	long long n;
+	__asm__ ("fcvt.l.d %0, %1, rmm" : "=r"(n) : "f"(x));
+	__asm__ ("fcvt.d.l %0, %1" : "=f"(tmp) : "r"(n));
+	// the sign bit is only copied to handle round(-0.0)
+	__asm__ ("fsgnj.d %0, %1, %2" : "=f"(x) : "f"(tmp), "f"(x));
+	return x;
+}
+
+#else
+
+#include "../round.c"
+
+#endif
diff --git a/src/math/riscv64/roundf.c b/src/math/riscv64/roundf.c
new file mode 100644
index 00000000..be588574
--- /dev/null
+++ b/src/math/riscv64/roundf.c
@@ -0,0 +1,21 @@
+#include <math.h>
+
+#if __riscv_flen >= 32
+
+float roundf(float x)
+{
+	if (!isfinite(x) || fabsf(x) >= 0x1p23) return x;
+	float tmp;
+	long n;
+	__asm__ ("fcvt.w.s %0, %1, rmm" : "=r"(n) : "f"(x));
+	__asm__ ("fcvt.s.w %0, %1" : "=f"(tmp) : "r"(n));
+	// the sign bit is only copied to handle round(-0.0)
+	__asm__ ("fsgnj.s %0, %1, %2" : "=f"(x) : "f"(tmp), "f"(x));
+	return x;
+}
+
+#else
+
+#include "../roundf.c"
+
+#endif
-- 
2.39.2