Added f24tof32 and f32tox (issue #29)

conversion/f24tof32.z80

@@ -0,0 +1,59 @@
+#ifndef included_f24tof32
+#define included_f24tof32
+#include "pushpop.z80"
+
+f24tof32:
+;convert an "f24" float to an IEEE-754 binary32
+;Input: AHL is the input float. BC points to where the f32 should be written.
+;Destroys: None
+  call pushpop
+  ex de,hl
+  ld h,b
+  ld l,c
+; Check for special values
+  ld c,a  ;save for the sign
+  add a,a
+  jr z,f24tof32_return_0
+  inc a
+  inc a
+  jr z,f24tof32_return_infnan
+  add a,126
+  rra
+  rl c
+  rra
+  rr d
+  rr e
+  ld (hl),0
+  rr (hl)
+  inc hl
+  ld (hl),e
+  inc hl
+  ld (hl),d
+  inc hl
+  ld (hl),a
+  ret
+f24tof32_return_0:
+  ld (hl),a
+  inc hl
+  ld (hl),a
+  inc hl
+  ld (hl),a
+  rra
+  inc hl
+  ld (hl),a
+  ret
+f24tof32_return_infnan:
+  ld a,d
+  or e
+  ld (hl),a
+  inc hl
+  ld (hl),a
+  inc hl
+  or %10000000
+  ld (hl),a
+  inc hl
+  ld a,c
+  or %01111111
+  ld (hl),a
+  ret
+#endif

conversion/f32tox.z80

@@ -0,0 +1,79 @@
+#ifndef included_f32tox
+#define included_f32tox
+#include "pushpop.z80"
+
+f32tox:
+;convert an IEEE-754 binary32 to an extended-precision float.
+;Input: HL points to the input float, BC points to where to output
+;Destroys: None
+  call pushpop
+  ld d,b
+  ld e,c
+  xor a
+  ld (de),a
+  inc de
+  ld (de),a
+  inc de
+  ld (de),a
+  inc de
+  ld (de),a
+  inc de
+  ld (de),a
+  inc de
+  ldi
+  ldi
+  ld a,(hl)
+  inc hl
+  ld c,a
+  or %10000000
+  ld (de),a
+  inc de
+  ld a,c
+  add a,a
+  ld a,(hl)
+  adc a,a
+  jr z,f32tox_return_0
+  inc a
+  jr z,f32tox_return_infnan
+;A-128+16384 is the exponent
+  rr c    ; save the sign
+  sub 128
+  ld (de),a
+  inc de
+  ld a,%10000000
+  sbc a,0
+  rl c
+  rra
+  ld (de),a
+  ret
+
+f32tox_return_infnan:
+  rr c  ; save the sign
+  ex de,hl
+  dec hl
+  ld a,(hl)
+  add a,a
+  dec hl
+  or (hl)
+  dec hl
+  or (hl)
+  inc hl
+  inc hl
+  sub 1   ; if A was 0 (inf),sets carry, else resets
+  ld a,$80
+  rra
+  ld (hl),a
+  xor a
+  ex de,hl
+  rl c  ; restore the sign
+  .db 1 ; start of `ld bc,**` to eat the next two bytes
+f32tox_return_0:
+  dec de
+  ld (de),a
+  inc de
+  ld (de),a
+  inc de
+  rra
+  ld (de),a
+  ret
+#endif