+++ /dev/null
-;
-; Fixed point sine function.
-;
-; Returns the cosine for the given argument as angular degree.
-; Valid argument range is 0..360
-;
-;
-; Ullrich von Bassewitz, 2009-10-29
-;
-
- .export _cc65_sin
-
- .import _cc65_sintab
-
-
-; ---------------------------------------------------------------------------
-;
-
-.code
-
-.proc _cc65_sin
-
-; If the high byte is non zero, argument is > 255
-
- cpx #0
- bne L3
- cmp #180
- bcs L4
-
-; 0..179°
-
- cmp #90
- bcc L1
-
-; 90..179°. Value is identical to sin(180-val). Carry is set on entry.
-;
-; 180-val := -val + 180.
-; With
-; -val := (val ^ $FF) + 1
-; we get
-; 180-val = (val ^ $FF) + 1 + 180
-; Since carry is set, we can drop the "+ 1".
-;
-
- eor #$FF
- adc #180 ; 180-val
-
-; 0..89°. Values for 87..90° are actually 1.0. Since this format doesn't fit
-; into the table, we have to check for it manually.
-
-L1: cmp #87
- bcc L2
-
-; The value is 1.0
-
- ldx #>(1 << 8)
- lda #<(1 << 8)
- rts
-
-; 0..86°. Read the value from the table.
-
-L2: tay
- ldx #0
- lda _cc65_sintab,y
- rts
-
-; 180..360°. sin(x) = -sin(x-180). Since the argument is in range 0..180
-; after the subtraction, we don't need to handle the high byte.
-
-L3: sec
-L4: sbc #180
-
- cmp #90
- bcc L5
-
-; 270..360°. Value is identical to -sin(180-val). Carry is set on entry.
-;
-; 180-val := -val + 180.
-; With
-; -val := (val ^ $FF) + 1
-; we get
-; 180-val = (val ^ $FF) + 1 + 180
-; Since carry is set, we can drop the "+ 1".
-;
-
- eor #$FF
- adc #180 ; 180-val
-
-; 180..269°. Values for 267..269° are actually -1.0. Since this format doesn't
-; fit into the table, we have to check for it manually.
-
-L5: ldx #$FF
- cmp #87
- bcc L6
-
-; The value is -1.0
-
- lda #<(-1 << 8)
- rts
-
-; 180..266°. Read the value from the table. Carry is clear on entry.
-
-L6: tay
- txa ; A = $FF
- eor _cc65_sintab,y
- adc #1
- bcc L7
- inx
-L7: rts
-
-.endproc
-
-
--- /dev/null
+;
+; Fixed point cosine/sine functions.
+;
+; Returns the cosine/sine for the given argument as angular degree.
+; Valid argument range is 0..360 for both functions. They will return
+; garbage if the argument is not in a valid range. Result is in 8.8 fixed
+; point format, so $100 is 1.0 and $FF00 is -1.0.
+;
+;
+; Ullrich von Bassewitz, 2009-10-29
+;
+
+ .export _cc65_cos, _cc65_sin
+
+
+; ---------------------------------------------------------------------------
+; Sinus table covering values from 0..86° as 0.8 fixed point values. Values
+; for 87..90° are actually 1.0 (= $100), will therefore not fit in the table
+; and are covered specially in the code below.
+
+.rodata
+
+_cc65_sintab:
+ .byte $00, $04, $09, $0D, $12, $16, $1B, $1F, $24, $28
+ .byte $2C, $31, $35, $3A, $3E, $42, $47, $4B, $4F, $53
+ .byte $58, $5C, $60, $64, $68, $6C, $70, $74, $78, $7C
+ .byte $80, $84, $88, $8B, $8F, $93, $96, $9A, $9E, $A1
+ .byte $A5, $A8, $AB, $AF, $B2, $B5, $B8, $BB, $BE, $C1
+ .byte $C4, $C7, $CA, $CC, $CF, $D2, $D4, $D7, $D9, $DB
+ .byte $DE, $E0, $E2, $E4, $E6, $E8, $EA, $EC, $ED, $EF
+ .byte $F1, $F2, $F3, $F5, $F6, $F7, $F8, $F9, $FA, $FB
+ .byte $FC, $FD, $FE, $FE, $FF, $FF, $FF
+
+
+
+; ---------------------------------------------------------------------------
+; Cosine function. Is actually implemented as cos(x) = sin(x+90)
+
+.code
+
+_cc65_cos:
+
+; cos(x) = sin(x+90)
+
+ clc
+ adc #90
+ bcc @L1
+ inx
+
+; If x is now larger than 360, we need to subtract 360.
+
+@L1: cpx #>360
+ bne @L2
+ cmp #<360
+@L2: bcc _cc65_sin
+
+ sbc #<360
+ bcs @L3
+ dex
+@L3: dex
+
+; ---------------------------------------------------------------------------
+; Sine function. Uses
+;
+; table lookup for 0..89°
+; sin(x) = sin(180-x) for 90°..179°
+; sin(x) = -sin(x-180) for 180..360°
+;
+; Plus special handling for the values missing in the table.
+
+_cc65_sin:
+
+; If the high byte is non zero, argument is > 255
+
+ cpx #0
+ bne L3
+ cmp #180
+ bcs L4
+
+; 0..179°
+
+ cmp #90
+ bcc L1
+
+; 90..179°. Value is identical to sin(180-val). Carry is set on entry.
+;
+; 180-val := -val + 180.
+; With
+; -val := (val ^ $FF) + 1
+; we get
+; 180-val = (val ^ $FF) + 1 + 180
+; Since carry is set, we can drop the "+ 1".
+;
+
+ eor #$FF
+ adc #180 ; 180-val
+
+; 0..89°. Values for 87..90° are actually 1.0. Since this format doesn't fit
+; into the table, we have to check for it manually.
+
+L1: cmp #87
+ bcc L2
+
+; The value is 1.0
+
+ ldx #>(1 << 8)
+ lda #<(1 << 8)
+ rts
+
+; 0..86°. Read the value from the table.
+
+L2: tay
+ ldx #0
+ lda _cc65_sintab,y
+ rts
+
+; 180..360°. sin(x) = -sin(x-180). Since the argument is in range 0..180
+; after the subtraction, we don't need to handle the high byte.
+
+L3: sec
+L4: sbc #180
+
+ cmp #90
+ bcc L5
+
+; 270..360°. Value is identical to -sin(180-val). Carry is set on entry.
+;
+; 180-val := -val + 180.
+; With
+; -val := (val ^ $FF) + 1
+; we get
+; 180-val = (val ^ $FF) + 1 + 180
+; Since carry is set, we can drop the "+ 1".
+;
+
+ eor #$FF
+ adc #180 ; 180-val
+
+; 180..269°. Values for 267..269° are actually -1.0. Since this format doesn't
+; fit into the table, we have to check for it manually.
+
+L5: ldx #$FF
+ cmp #87
+ bcc L6
+
+; The value is -1.0
+
+ lda #<(-1 << 8)
+ rts
+
+; 180..266°. Read the value from the table. Carry is clear on entry.
+
+L6: tay
+ txa ; A = $FF
+ eor _cc65_sintab,y
+ adc #1
+ bcc L7
+ inx
+L7: rts
+
+
+++ /dev/null
-;
-; Sinus table
-;
-; Ullrich von Bassewitz, 2009-10-29
-;
-
- .export _cc65_sintab
-
-
-; ---------------------------------------------------------------------------
-;
-
-.rodata
-
-_cc65_sintab:
- .byte $00, $04, $09, $0D, $12, $16, $1B, $1F, $24, $28
- .byte $2C, $31, $35, $3A, $3E, $42, $47, $4B, $4F, $53
- .byte $58, $5C, $60, $64, $68, $6C, $70, $74, $78, $7C
- .byte $80, $84, $88, $8B, $8F, $93, $96, $9A, $9E, $A1
- .byte $A5, $A8, $AB, $AF, $B2, $B5, $B8, $BB, $BE, $C1
- .byte $C4, $C7, $CA, $CC, $CF, $D2, $D4, $D7, $D9, $DB
- .byte $DE, $E0, $E2, $E4, $E6, $E8, $EA, $EC, $ED, $EF
- .byte $F1, $F2, $F3, $F5, $F6, $F7, $F8, $F9, $FA, $FB
- .byte $FC, $FD, $FE, $FE, $FF, $FF, $FF
projects / cc65 / commitdiff