Update sin_FAC1

STATUS.md

@@ -263,7 +263,7 @@ Floating point mathematical routines - not official, but well known and broadly
 | `$E09A`   | `rnd_A`                | DONE     |                                                    |
 | `$E0BE`   | `rnd_generate`         | DONE     |                                                    |
 | `$E264`   | `cos_FAC1`             | DONE     | From the Microsoft BASIC, original name: COS       |
-| `$E26B`   | `sin_FAC1`             | PARTIAL  | not fully tested yet                               |
+| `$E26B`   | `sin_FAC1`             | DONE     | From the Microsoft BASIC, original name: SIN       |
 | `$E2B4`   | `tan_FAC1`             | PARTIAL  | not fully tested yet                               |
 | `$E30E`   | `atn_FAC1`             | DONE     | From the Microsoft BASIC, original name: ATN       |
 

src/basic/math_trans/e26b.sin_FAC1.s

@@ -2,9 +2,22 @@
 ;; #LAYOUT# *   BASIC_0 #TAKE
 ;; #LAYOUT# *   *       #IGNORE
 
-;
+; This file is under the MIT license, it contains code released by Microsoft Corporation.
+; See LICENSE for more information.
+
 ; Math package - sine of FAC1 in radians
 ;
+; This is verified to be identical to the original Microsoft implementation where it was named SIN.
+;
+; USE IDENTITIES TO GET FAC IN QUADRANTS I OR IV.
+; THE FAC IS DIVIDED BY 2*PI AND THE INTEGER PART IS IGNORED
+; BECAUSE SIN(X+2*PI)=SIN(X). THEN THE ARGUMENT CAN BE COMPARED
+; WITH PI/2 BY COMPARING THE RESULT OF THE DIVISION
+; WITH PI/2/(2*PI)=1/4.
+; IDENTITIES ARE THEN USED TO GET THE RESULT IN QUADRANTS
+; I OR IV. AN APPROXIMATION POLYNOMIAL IS THEN USED TO
+; COMPUTE SIN(X).
+;
 ; See also:
 ; - [CM64] Computes Mapping the Commodore 64 - page 210 - XXX address does not match
 ; - https://www.c64-wiki.com/wiki/Floating_point_arithmetic
@@ -17,44 +30,41 @@
 
 sin_FAC1:
 
-    jsr mov_FAC1_FAC2               ; FAC1 <- X / (2*pi)     (X2)
+        jsr mov_r_FAC1_FAC2
-    ldy #>const_DOUBLE_PI
+        lda #<const_DOUBLE_PI       ; Get pointer to divisor
-    lda #<const_DOUBLE_PI
+        ldy #>const_DOUBLE_PI
-    jsr mov_MEM_FAC1
+        ldx FAC2_sign               ; Get sign of result
-    jsr div_FAC2_FAC1
+        jsr div_FAC2_MEM
-
+        jsr mov_r_FAC1_FAC2         ; Get result into FAC2
-    jsr mov_FAC1_FAC2               ; FAC2 <- X2
+        jsr int_FAC1
-    jsr int_FAC1                    ; FAC1 <- INT(X2)
+        lda #$00
-    jsr sub_FAC2_FAC1               ; FAC1 <- X2 - INT(X2)   (F)
+        sta ARISGN                  ; Always have the same sign
-
+        jsr sub_FAC2_FAC1           ; Keep only the fractional part
-    ldy #>const_QUARTER
+        lda #<const_QUARTER         ; Get pointer to 1/4
-    lda #<const_QUARTER
+        ldy #>const_QUARTER
-    jsr FCOMP
+        jsr sub_MEM_FAC1            ; Compute 1/4 - FAC1
-    bmi sin_next                    ; FAC1 < 0.25
+        lda FAC1_sign               ; Save sign for later
-
+        pha
-    ldy #>sin_three_quarters
+        bpl SIN1                    ; First quadrant
-    lda #<sin_three_quarters
+        jsr add_HALF_FAC1           ; Add 1/2 to FAC1
-    jsr FCOMP
+        lda FAC1_sign               ; Sign is negative?
-    bmi sin_q23                     ; FAC1 < 0.75
+        bmi SIN2
-
+        lda TANSGN                  ; Quadrants II and III come here
-    jsr mov_FAC1_FAC2               ; FAC1 <- FAC1 - 1.0
+        eor #$FF
-    ldy #>const_ONE
+        sta TANSGN
-    lda #<const_ONE
+SIN1:
-    jsr mov_MEM_FAC1
+        jsr toggle_sign_FAC1        ; If positive, negate it
-    jsr sub_FAC2_FAC1
+SIN2:
-    +bra sin_next
+        lda #<const_QUARTER         ; Get pointer to 1/4
-
+        ldy #>const_QUARTER
-sin_q23:
+        jsr add_MEM_FAC1            ; Add it in
-    ldy #>const_HALF
+        pla                         ; Get original quadrant
-    lda #<const_HALF
+        bpl SIN3
-    jsr sub_MEM_FAC1                ; FAC1 <- 0.5 - FAC1
+        jsr toggle_sign_FAC1        ; If negative, negate result
-
+SIN3:
-    ; FALLTHROUGH
+        lda #<poly_sin
-    
+        ldy #>poly_sin
-sin_next:
+        jmp poly1_FAC1              ; Do approximation polynomial
-    ldy #>poly_sin
-    lda #<poly_sin
-    jmp poly1_FAC1
 
 
 } else {

tools/similarity.c

@@ -32,7 +32,7 @@ unsigned short microsoft_basic_chunks[NUM_CHUNKS * 2] = {
     0xBDB3, 0xBDC1,
     0xBDDD, 0xBF51,
     0xBFB4, 0xBFEC,
-    0xE264, 0xE26A,
+    0xE264, 0xE2B3,
     0xE2EF, 0xE37A,
 };