LibC: add math.h with floorl

libc/CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.26)
 
-project(libc CXX)
+project(libc CXX ASM)
 
 set(LIBC_SOURCES
 	ctype.cpp
@@ -10,6 +10,7 @@ set(LIBC_SOURCES
 	stdlib.cpp
 	string.cpp
 	unistd.cpp
+	math.S
 )
 
 add_custom_target(libc-headers

libc/include/math.h

@@ -0,0 +1,9 @@
+#pragma once
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+long double floorl(long double);
+
+__END_DECLS

libc/math.S

@@ -0,0 +1,26 @@
+
+.global floorl;
+floorl:
+	fldt	8(%rsp)
+
+	fnstenv	-28(%rsp)		/* store fpu environment */
+
+	/* We use here %edx although only the low 1 bits are defined.
+	  But none of the operations should care and they are faster
+	  than the 16 bit operations.  */
+	movl	$0x400,%edx		/* round towards -oo */
+	orl	-28(%rsp),%edx
+	andl	$0xf7ff,%edx
+	movl	%edx,-32(%rsp)
+	fldcw	-32(%rsp)		/* load modified control word */
+
+	frndint				/* round */
+
+	/* Preserve "invalid" exceptions from sNaN input.  */
+	fnstsw
+	andl	$0x1, %eax
+	orl	%eax, -24(%rsp)
+
+	fldenv	-28(%rsp)		/* restore original environment */
+
+	ret