math.nbtheory: Implement natural logarithm

arch/build.ninja

@@ -5,9 +5,10 @@ rule archive
   command = ar rcs $out $in
 
 build abs.o: gas x64/linux/math/abs.S
+build log.o: gas x64/linux/math/log.S
 build cmp.o: gas x64/linux/memory/cmp.S
 build fill.o: gas x64/linux/memory/fill.S
 build copy.o: gas x64/linux/memory/copy.S
 build syscall.o: gas x64/linux/syscall.S
 
-build tanya.a: archive syscall.o copy.o fill.o cmp.o abs.o
+build tanya.a: archive syscall.o copy.o fill.o cmp.o log.o abs.o

arch/x64/linux/math/log.S

@@ -0,0 +1,48 @@
+	.text
+
+
+// logl.
+	.globl _D5tanya4math8nbtheory2lnFNaNbNiNfeZe
+	.type _D5tanya4math8nbtheory2lnFNaNbNiNfeZe, @function
+
+_D5tanya4math8nbtheory2lnFNaNbNiNfeZe:
+	fldln2 // Put lb(e) onto the FPU stack
+	fldt 8(%rsp) // Put the argument onto the FPU stack
+	fyl2x // %st1 * lb(%st0)
+	ret
+
+
+// log.
+	.globl _D5tanya4math8nbtheory2lnFNaNbNiNfdZd
+	.type _D5tanya4math8nbtheory2lnFNaNbNiNfdZd, @function
+
+_D5tanya4math8nbtheory2lnFNaNbNiNfdZd:
+	movsd %xmm0, -8(%rsp) // Put the argument onto the stack
+
+	fldln2 // Put lb(e) onto the FPU stack
+	fldl -8(%rsp) // Put a double onto the FPU stack
+	fyl2x // %st1 * lb(%st0)
+
+	 // The result is on the FPU stack, but returned in %xmm0
+	fstpl -8(%rsp)
+	movsd -8(%rsp), %xmm0
+
+	ret
+
+
+// logf.
+	.globl _D5tanya4math8nbtheory2lnFNaNbNiNffZf
+	.type _D5tanya4math8nbtheory2lnFNaNbNiNffZf, @function
+
+_D5tanya4math8nbtheory2lnFNaNbNiNffZf:
+	movss %xmm0, -4(%rsp) // Put the argument onto the stack
+
+	fldln2 // Put lb(e) onto the FPU stack
+	flds -4(%rsp) // Put a float onto the FPU stack
+	fyl2x // %st1 * lb(%st0)
+
+	 // The result is on the FPU stack, but returned in %xmm0
+	fstps -4(%rsp)
+	movss -4(%rsp), %xmm0
+
+	ret