Fixed bug causing negative integers to be rounded down by 1

Author: Zeda

conversion/f32toi16.z80

@@ -11,70 +11,91 @@ f32toi16:
  push de
  push bc
  push af
- ld e,(hl)
+
+ ld c,(hl)
  inc hl
- ld d,(hl)
+ ld e,(hl)
  inc hl
  ld a,(hl)
  rlca
  scf
  rra
- ld c,a
+ ld d,a
  inc hl
  ld a,(hl)
  adc a,a
-
-; carry flag is sign, CDE is the significand, A is the exponent
- push af ; carry flag is a sign
-
+; carry flag is sign, DEC is the significand, A is the exponent
  call f32toi16_get_int
-
- pop af ; get the carry flag
- ld a,h
- jr nc,f32toi16_return
- ; -HL-1
- ld a,l
- cpl
- ld l,a
- ld a,h
- cpl
- ld h,a
 f32toi16_return:
  pop af
  pop bc
  pop de
  ret
 
 f32toi16_get_int:
- ld hl,32767
+ rl b ; save the sign
  cp 142
- ret nc
- sub h ;
+ jr nc,f32toi16_return_early
+ sub 127
  ld hl,0
  ret c
- ld b,a
 
  ; if the exponent is 128, return 0 if NaN, else inf
  jp p,f32toi16_extract
- ld a,l
+ ld a,c
  or e
  or d
  ret nz
+f32toi16_return_early:
  ld hl,32767
+ rr b
+ ret nc
+ inc hl
  ret
+
 f32toi16_extract:
+ ex de,hl ; significand is in HLC now, but we don't need to track C
+ ;DE is 0
+ cp 7
+ jr c,$+7
+ ;shift up by 8
+ sub 8
+ ld e,h
+ ld h,l
+ ld l,d ; 0
+
+ ld d,b ; save sign
+ ld b,a
  inc b
- ld l,d
- ld h,c
  xor a
- ld e,a
+ ;AE.HLC
 
  add hl,hl
  rl e
  rla
  djnz $-4
 
+ ld b,d ; save sign again
+ ld d,a
+ ex de,hl
+ ; HL is the result, DEC has any fractional bits
+
+ rrc b ; if carry is reset, then we are done
+ ret nc
+ ; otherwise the number is negative, so if the fractional part is non-zero,
+ ; need to round down
+
+ xor a
+ sub l
+ ld l,a
+ sbc a,a
+ sub h
  ld h,a
- ld l,e
+
+ ld a,c
+ or d
+ or e
+ ret z
+ dec hl
  ret
 #endif

conversion/f32toi8.z80

@@ -12,9 +12,10 @@ f32toi8:
  push hl
  push de
  push bc
- ld e,(hl)
+ ld a,(hl)
  inc hl
- ld d,(hl)
+ or (hl)
+ ld d,a ; save the OR of the bottom two bytes of the significand
  inc hl
  ld a,(hl)
  rlca
@@ -25,42 +26,51 @@ f32toi8:
  ld a,(hl)
  adc a,a
 
-; carry flag is sign, CDE is the significand, A is the exponent
- push af ; carry flag is a sign
+ rr e ; save the sign
+; E has the sign, C is the portion of the significand that matters,
+; A is the exponent
 
  call f32toi8_get_int
 
- pop af ; get the carry flag
- ; if carry is set, return -H-1, else return H
- sbc a,a
- xor h
 f32toi8_return:
  pop bc
  pop de
  pop hl
  ret
 
 f32toi8_get_int:
- ld h,127
  cp 134
- ret nc
- sub h
+ jr nc,f32toi8_return_inf
+ sub 127
  ld h,0
  ret c
- ld l,c ; upper 8 bits of the significand
- ld b,a
 
  ; if the exponent is 128, return inf
  jp p,f32toi8_extract
  ld a,l
  or e
  or d
  ret nz
+f32toi8_return_inf:
  ld h,127
+ rl e
+ ret nc
+ inc h
  ret
+
 f32toi8_extract:
+ ld l,c ; upper 8 bits of the significand, H is 0
+ ld b,a
  inc b
  add hl,hl
  djnz $-1
+ rl e
+ ret nc
+ ld a,l
+ or d
+ add a,255
+ sbc a,a
+ sub h
+ ld h,a
  ret
 #endif