Moved fixed point multiplication and rounding into an asm module.

git-svn-id: svn://svn.cc65.org/cc65/trunk@4447 b7a2c559-68d2-44c3-8de9-860c34a00d81
2009-11-05 20:16:43 +00:00
parent de6050f21d
commit 787f069738
6 changed files with 75 additions and 17 deletions
--- a/libsrc/tgi/tgi_imulround.s
+++ b/libsrc/tgi/tgi_imulround.s
@@ -0,0 +1,54 @@
+;
+; Ullrich von Bassewitz, 2009-11-05
+;
+; Helper function for functions using sine/cosine: Multiply two values, one
+; being an 8.8 fixed point one, and return the rounded and scaled result.
+;
+
+
+        .export         _tgi_imulround
+        .import         popax, imul16x16r32
+
+        .include        "zeropage.inc"
+
+
+;----------------------------------------------------------------------------
+;
+
+.code
+.proc   _tgi_imulround
+
+; Get arguments
+
+        sta     ptr1
+        stx     ptr1+1                  ; Save lhs
+        jsr     popax                   ; Get rhs
+
+; Multiplicate
+
+        jsr     imul16x16r32
+
+; Round the result
+
+        cmp     #$80                    ; Frac(x) >= 0.5?
+        txa
+        ldy     sreg+1                  ; Check sign
+        bmi     @L1
+
+        adc     #$00
+        tay
+        lda     sreg
+        adc     #$00
+        tax
+        tya
+        rts
+
+@L1:    sbc     #$00
+        tay
+        lda     sreg
+        sbc     #$00
+        tax
+        tya
+        rts
+
+.endproc