[CRT:MATH] Import nextafter, nextafterf and nexttowardf from musl

Note: On Windows, where a long double is the same as a double, nextafterl is the same as nextafter, nexttowardl is the same as nexttoward.
Also nexttoward is the same as nextafter.

Author: tkreuzer

dll/win32/crtdll/crtdll.spec

@@ -236,7 +236,7 @@
 @ cdecl _mkdir(str)
 @ cdecl _mktemp(str)
 @ cdecl _msize(ptr)
-@ cdecl _nextafter(double double)
+@ cdecl _nextafter(double double) nextafter
 @ cdecl _onexit(ptr)
 @ varargs _open(str long)
 @ cdecl _open_osfhandle(long long)

dll/win32/msvcrt/msvcrt.spec

@@ -882,8 +882,8 @@
 @ cdecl _mktime64(ptr)
 @ cdecl _msize(ptr)
 @ stub -version=0x600+ -arch=i386 _msize_debug
-@ cdecl _nextafter(double double)
-@ stub -arch=x86_64 _nextafterf
+@ cdecl _nextafter(double double) nextafter
+@ cdecl -arch=!i386 _nextafterf(long) nextafterf
 @ extern _onexit # Declaring it as extern let us use the symbol from msvcrtex while having the __imp_ symbol defined in the import lib
 @ varargs _open(str long)
 @ cdecl _open_osfhandle(long long)

dll/win32/msvcrt20/msvcrt20.spec

@@ -739,7 +739,7 @@
 @ cdecl _msize(ptr)
 @ stub _mtlock
 @ stub _mtunlock
-@ cdecl _nextafter(double double)
+@ cdecl _nextafter(double double) nextafter
 @ cdecl _onexit(ptr)
 @ varargs _open(str long)
 @ cdecl _open_osfhandle(long long)

dll/win32/msvcrt40/msvcrt40.spec

@@ -800,7 +800,7 @@
 @ cdecl _msize(ptr)
 @ stub _mtlock
 @ stub _mtunlock
-@ cdecl _nextafter(double double)
+@ cdecl _nextafter(double double) nextafter
 @ cdecl _onexit(ptr)
 @ varargs _open(str long)
 @ cdecl _open_osfhandle(long long)

dll/win32/ucrtbase/ucrtbase.spec

@@ -1792,9 +1792,9 @@
 @ cdecl _o_nextafter(double double) nextafter
 @ cdecl _o_nextafterf(float float) nextafterf
 @ cdecl _o_nextafterl(double double) nextafter
-@ cdecl _o_nexttoward(double double) nexttoward
+@ cdecl _o_nexttoward(double double) nextafter
 @ cdecl _o_nexttowardf(float double) nexttowardf
-@ cdecl _o_nexttowardl(double double) nexttoward
+@ cdecl _o_nexttowardl(double double) nextafter
 @ cdecl _o_pow(double double) pow
 @ cdecl -arch=!i386 _o_powf(float float) powf
 @ cdecl _o_putc(long ptr) putc
@@ -2511,12 +2511,12 @@
 @ cdecl -stub nearbyint(double)
 @ cdecl -stub nearbyintf(float)
 @ cdecl nearbyintl(double) nearbyint
-@ cdecl -stub nextafter(double double)
-@ cdecl -stub nextafterf(float float)
+@ cdecl nextafter(double double)
+@ cdecl nextafterf(float float)
 @ cdecl nextafterl(double double) nextafter
-@ cdecl -stub nexttoward(double double) nexttoward
-@ cdecl -stub nexttowardf(float double) nexttowardf
-@ cdecl nexttowardl(double double) nexttoward
+@ cdecl nexttoward(double double) nextafter
+@ cdecl nexttowardf(float double)
+@ cdecl nexttowardl(double double) nextafter
 @ stub norm
 @ stub normf
 @ stub norml

sdk/lib/crt/float/float.cmake

@@ -6,7 +6,6 @@ list(APPEND CRT_FLOAT_SOURCE
     float/copysign.c
     float/fpclass.c
     float/fpecode.c
-    float/nafter.c
     float/scalb.c
 )
 

sdk/lib/crt/float/nafter.c

@@ -0,0 +1,70 @@
+//
+// libm.h
+//
+//      Partly imported from musl libc
+//
+// Support header for musl math code.
+//
+// SPDX-License-Identifier: MIT
+//
+
+#pragma once
+
+#include <stdint.h>
+#include <float.h>
+#include <math.h>
+
+// Define _STATIC_ASSERT for compatibility with legacy CRT headers
+#ifndef _STATIC_ASSERT
+#define _STATIC_ASSERT(expr) extern char (*__static_assert__(void)) [(expr) ? 1 : -1]
+#endif
+
+// Make sure the sizes are correct
+_STATIC_ASSERT(sizeof(float) == 4);
+_STATIC_ASSERT(sizeof(double) == 8);
+_STATIC_ASSERT(sizeof(long double) == 8);
+
+_Check_return_ int __cdecl _isnanf(_In_ float _X);
+#define isnan _isnan
+#define isnanf _isnanf
+
+// musl has this in math.h
+static __inline uint32_t __FLOAT_BITS(float __f)
+{
+	union {float __f; uint32_t __i;} __u;
+	__u.__f = __f;
+	return __u.__i;
+}
+
+static __inline uint64_t __DOUBLE_BITS(double __f)
+{
+	union {double __f; uint64_t __i;} __u;
+	__u.__f = __f;
+	return __u.__i;
+}
+
+#define signbit(x) \
+	((sizeof(x) == sizeof(float)) ? (int)(__FLOAT_BITS(x)>>31) : \
+	                                (int)(__DOUBLE_BITS(x)>>63))
+
+static inline void fp_force_evalf(float x)
+{
+	volatile float y;
+	y = x;
+    (void)y;
+}
+
+static inline void fp_force_eval(double x)
+{
+	volatile double y;
+	y = x;
+    (void)y;
+}
+
+#define FORCE_EVAL(x) do {                    \
+	if (sizeof(x) == sizeof(float)) {         \
+		fp_force_evalf(x);                    \
+	} else {                                  \
+		fp_force_eval(x);                     \
+	}                                         \
+} while(0)

sdk/lib/crt/math/libm.h

@@ -14,6 +14,9 @@ list(APPEND LIBCNTPR_MATH_SOURCE
     math/div.c
     math/exp2f.c
     math/labs.c
+    math/nextafter.c
+    math/nextafterf.c
+    math/nexttowardf.c
     math/round.c
     math/roundf.c
     math/scalbn.c

sdk/lib/crt/math/math.cmake

@@ -0,0 +1,41 @@
+/*
+ * PROJECT:     ReactOS CRT
+ * LICENSE:     MIT (https://spdx.org/licenses/MIT)
+ * PURPOSE:     Implementation of nextafter.
+ * COPYRIGHT:   Imported from musl libc
+ *              https://git.musl-libc.org/cgit/musl/tree/src/math/nextafter.c
+ *              blob: ab5795a47a93e36c8c461d8a4be6621b582ae077
+ *              See https://git.musl-libc.org/cgit/musl/tree/COPYRIGHT
+ */
+
+#include "libm.h"
+
+double nextafter(double x, double y)
+{
+	union {double f; uint64_t i;} ux={x}, uy={y};
+	uint64_t ax, ay;
+	int e;
+
+	if (isnan(x) || isnan(y))
+		return x + y;
+	if (ux.i == uy.i)
+		return y;
+	ax = ux.i & ~0ULL/2;
+	ay = uy.i & ~0ULL/2;
+	if (ax == 0) {
+		if (ay == 0)
+			return y;
+		ux.i = (uy.i & 1ULL<<63) | 1;
+	} else if (ax > ay || ((ux.i ^ uy.i) & 1ULL<<63))
+		ux.i--;
+	else
+		ux.i++;
+	e = ux.i >> 52 & 0x7ff;
+	/* raise overflow if ux.f is infinite and x is finite */
+	if (e == 0x7ff)
+		FORCE_EVAL(x+x);
+	/* raise underflow if ux.f is subnormal or zero */
+	if (e == 0)
+		FORCE_EVAL(x*x + ux.f*ux.f);
+	return ux.f;
+}