feat(isprime): Implement modulo operation

One implementation as macro, where we're dividing by a constant and a
procedure where we're diving by memory value

1 files changed, 41 insertions, 6 deletions

diff --git a/isprime/isprime.oph.s b/isprime/isprime.oph.s
index 9fbc15e..e4824fa 100644
--- a/isprime/isprime.oph.s
+++ b/isprime/isprime.oph.s
@@ -6,16 +6,51 @@
 .require "basic_starter.oph.s"
 .require "kernal.oph.s"
 
-number:  .word 1
+number:  .word 15
 
 main:
          `lowercase
-         lda number
+         jsr isprime ; a = isprime(number)
          bne +       ; if (a == 0)
-         `print yes
-         rts
-*        `print no
-         rts
+         `print no   ;   print "No"
+         rts         ;   return
+*        `print yes  ; else print "Yes"
+         rts         ;   return
+
+isprime:
+.scope
+         lda #1         ; if (number & 0b0001 == 0)
+         and number
+         beq _end       ;   return False
+         ;`mod number, 3 ; if (number % 3 == 0)
+         ;beq _end       ;   return False
+         lda number
+         ldx #3
+         stx mod_n
+         jsr mod_addr
+_end:    rts
+.scend
+
+.macro mod ; 12 cycles (2+4+2+2+2) raw
+         sec       ; carry = 0
+         lda _1    ; a = _1
+_loop:   sbc #_2   ; do  a -= _2 + carry
+         beq _end  ;     if (a == 0) break
+         bpl _loop ; while (a >= 0)
+_end:
+.macend
+
+mod_n:   .word 0
+
+; a % mod_n
+mod_addr: ; 16 cycles (2+4+2+2+6) raw + 18 cycles (4+4+4+6) raw for arguments
+.scope
+         sec       ; carry = 0
+_loop:   sbc mod_n ; do  a -= mod_n + carry
+         beq _end  ;     if (a == 0) break
+         bpl _loop ; while (a >= 0)
+_end:    rts
+.scend
 
 .charmap 'A, "abcdefghijklmnopqrstuvwxyz"
 .charmap 'a, "ABCDEFGHIJKLMNOPQRSTUVWXYZ"