optimized frexpf slightly

Author: ZERICO2005

src/libc/frexpf.src

@@ -15,6 +15,7 @@ else
 _frexp:
 _frexpf:
 	ld	iy, 0
+	lea	de, iy - 127	; bias	; $FFFF81
 	add	iy, sp
 	ld	hl, (iy + 3)
 	add	hl, hl
@@ -29,7 +30,7 @@ _frexpf:
 	rr	b
 	sbc	hl, hl
 	ld	l, a
-	ld	de, -127	; bias
+;	ld	de, -127	; bias
 	add	hl, de
 .ret_subnormal:
 	res	7, (iy + 5)
@@ -47,22 +48,22 @@ _frexpf:
 	jr	.ret_self
 
 .maybe_subnormal:
-	add	hl, bc
-	or	a, a
-	sbc	hl, bc
-	jr	z, .ret_zero
+	ld	e, d	; ld de, -1
+	add	hl, de
+	inc	hl	; restore HL
+	jr	nc, .ret_zero
 	; input: HL output: A
 	call	__ictlz
 	ld	c, a
 	call	__ishl
 	ld	(iy + 3), hl
-	scf
-	sbc	hl, hl
+	sub	a, 131	; (127 + 3) + 1? idk where this magic number comes from
 	cpl
-	add	a, 131	; 127 + 3 + 1? idk where this magic number comes from
+	sbc	hl, hl	; Carry is set here
 	ld	l, a
-	ld	a, b	; exponent
-	xor	a, $3F
+	; copy exponent of 0.5f
+	ld	a, b
+	xor	a, $3F	
 	ld	b, a
 	jr	.ret_subnormal
 

test/floating_point/float32_frexp/src/main.c

@@ -31,8 +31,10 @@ 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);
+                #if 0
+                    printf("G: %08lX %d\n", result.bin, expon);
+                    printf("T: %08lX %d\n", output[i].frac.bin, output[i].expon);
+                #endif
                 return i;
             }
         }