Implemented frexpf in assembly (with subnormal support)

Author: ZERICO2005

src/libc/frexpf.c

@@ -1,6 +1,7 @@
 	assume	adl=1
 
 	section	.text
+
 	public	_frexpf
 	public	_frexp
 
@@ -11,10 +12,61 @@ _frexp := _frexpf
 
 else
 
-_frexpf := __frexpf_c
-_frexp := __frexp_c
+_frexp:
+_frexpf:
+	ld	iy, 0
+	add	iy, sp
+	ld	hl, (iy + 3)
+	add	hl, hl
+	ld	b, (iy + 6)
+	ld	a, b
+	adc	a, a
+	jr	z, .maybe_subnormal
+	inc	a
+	jr	z, .inf_nan
+	; normal
+	ld	b, $7E	; $3F << 1
+	rr	b
+	sbc	hl, hl
+	ld	l, a
+	ld	de, -127	; bias
+	add	hl, de
+.ret_subnormal:
+	res	7, (iy + 5)
+.ret_zero:
+.ret_self:
+	ld	de, (iy + 9)	; int *expon
+	ex	de, hl
+	ld	(hl), de
+	ld	hl, (iy + 3)	; mantissa
+	ld	e, b	; exponent
+	ret
+
+.inf_nan:
+	ld	hl, $7FFFFF ; INT_MAX
+	jr	.ret_self
+
+.maybe_subnormal:
+	add	hl, bc
+	or	a, a
+	sbc	hl, bc
+	jr	z, .ret_zero
+	; input: HL output: A
+	call	__ictlz
+	ld	c, a
+	call	__ishl
+	ld	(iy + 3), hl
+	scf
+	sbc	hl, hl
+	neg
+	add	a, 130	; 127 + 3? idk where this magic number comes from
+	ld	l, a
+	ld	a, b	; exponent
+	xor	a, $3F
+	ld	b, a
+	jr	.ret_subnormal
 
-	extern	__frexpf_c
-	extern	__frexp_c
+	extern	__ictlz
+	extern	__ishl
 
 end if

src/libc/frexpf.src

@@ -8,9 +8,6 @@
 #include <ti/getcsc.h>
 #include <sys/util.h>
 
-/* enable if the toolchain is configured to use the subnormal compliant frexpf */
-#if 0
-
 #include "f32_frexp_LUT.h"
 
 #define ARRAY_LENGTH(x) (sizeof(x) / sizeof(x[0]))
@@ -34,6 +31,8 @@ size_t run_test(void) {
         result.flt = frexpf(input[i], &expon);
         if (result.bin != output[i].frac.bin || expon != output[i].expon) {
             if (!(isnan(result.flt) && isnan(output[i].frac.flt))) {
+                // printf("G: %08lX %d\n", result.bin, expon);
+                // printf("T: %08lX %d\n", output[i].frac.bin, output[i].expon);
                 return i;
             }
         }
@@ -56,14 +55,3 @@ int main(void) {
 
     return 0;
 }
-
-#else
-
-int main(void) {
-    os_ClrHome();
-    printf("All tests passed");
-    while (!os_GetCSC());
-    return 0;
-}
-
-#endif