math: Add floating point support to abs

arch/build.ninja

@@ -4,6 +4,7 @@ rule gas
 rule archive
   command = ar rcs $out $in
 
+build abs.o: gas x64/linux/math/abs.S
 build syscall.o: gas x64/linux/syscall.S
 
-build tanya.a: archive syscall.o
+build tanya.a: archive syscall.o abs.o

arch/x64/linux/math/abs.S

@@ -0,0 +1,35 @@
+	.text
+
+
+// fabsf.
+	.globl _D5tanya4math8nbtheory10__T3absTfZ3absFNaNbNiNffZf
+	.type _D5tanya4math8nbtheory10__T3absTfZ3absFNaNbNiNffZf, @function
+
+_D5tanya4math8nbtheory10__T3absTfZ3absFNaNbNiNffZf:
+	mov $0x7fffffff, %eax
+	movq %rax, %xmm1
+	andpd %xmm1, %xmm0
+	ret
+
+
+// fabs.
+	.globl _D5tanya4math8nbtheory10__T3absTdZ3absFNaNbNiNfdZd
+	.type _D5tanya4math8nbtheory10__T3absTdZ3absFNaNbNiNfdZd, @function
+
+_D5tanya4math8nbtheory10__T3absTdZ3absFNaNbNiNfdZd:
+	mov $0x7fffffffffffffff, %rax
+	movq %rax, %xmm1
+	andpd %xmm1, %xmm0
+	ret
+
+
+// fabsl.
+	.globl _D5tanya4math8nbtheory10__T3absTeZ3absFNaNbNiNfeZe
+	.type _D5tanya4math8nbtheory10__T3absTeZ3absFNaNbNiNfeZe, @function
+
+// Load the parameter from the stack onto FP stack, execute 'fabs' instruction
+// The result is returned in ST0.
+_D5tanya4math8nbtheory10__T3absTeZ3absFNaNbNiNfeZe:
+	fldt 0x8(%rsp)
+	fabs
+	ret