[musl] [PATCH 2/2] math: add riscv64 round/roundf

[musl] [PATCH 2/2] math: add riscv64 round/roundf

[Meng Zhuo]

---
 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..12e670a5
--- /dev/null
+++ b/src/math/riscv64/round.c
@@ -0,0 +1,21 @@
+#include <math.h>
+
+#if __riscv_flen >= 64
+
+double round(double x)
+{
+	if (isnan(x)) return x;
+	if (x == INFINITY || x == -INFINITY) 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));
+	x = copysign(tmp, 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..8da3c65a
--- /dev/null
+++ b/src/math/riscv64/roundf.c
@@ -0,0 +1,21 @@
+#include <math.h>
+
+#if __riscv_flen >= 32
+
+float roundf(float x)
+{
+	if (isnan(x)) return x;
+	if (x == INFINITY || x == -INFINITY) 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));
+	x = copysign(tmp, x);		
+	return x;
+}
+
+#else
+
+#include "../roundf.c"
+
+#endif
-- 
2.39.2

Re: [musl] [PATCH 2/2] math: add riscv64 round/roundf

[Rich Felker]

On Wed, Jun 12, 2024 at 05:00:18PM +0800, Meng Zhuo wrote:
> ---
>  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..12e670a5
> --- /dev/null
> +++ b/src/math/riscv64/round.c
> @@ -0,0 +1,21 @@
> +#include <math.h>
> +
> +#if __riscv_flen >= 64
> +
> +double round(double x)
> +{
> +	if (isnan(x)) return x;
> +	if (x == INFINITY || x == -INFINITY) 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));
> +	x = copysign(tmp, 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..8da3c65a
> --- /dev/null
> +++ b/src/math/riscv64/roundf.c
> @@ -0,0 +1,21 @@
> +#include <math.h>
> +
> +#if __riscv_flen >= 32
> +
> +float roundf(float x)
> +{
> +	if (isnan(x)) return x;
> +	if (x == INFINITY || x == -INFINITY) 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));
> +	x = copysign(tmp, x);		
> +	return x;
> +}
> +
> +#else
> +
> +#include "../roundf.c"
> +
> +#endif
> -- 
> 2.39.2

These functions clearly have the wrong behavior for inputs like
0x1p1000. As a general principle, you can't implement round in terms
of lround/llround, only the opposite direction. You may be able to do
it by first performing a range check, though. For example,

	if (!(fabs(x) < 0x1p54)) return x;

Note that this also covers the non-finite cases, but I'm not sure if
it avoids raising exceptions it shouldn't. If not, or if you weren't
doing this, you can collapse the multiple inf/nan checks you have to:

	if (!isfinite(x)) return x;

You should also probably use copysignf rather than copysign for
roundf, or do an inline version of it.

Rich