From 4b4c1a130a3ef64f3f788e2ebd46cfc3b0e121fc Mon Sep 17 00:00:00 2001
From: Syndamia <kamen@syndamia.com>
Date: Fri, 1 Aug 2025 12:40:20 +0300
Subject: feat(isprime): Clean up and add comments for implementation

---
 isprime/isprime.oph.s | 85 +++++++++++++++++++++++++--------------------------
 isprime/kernal.oph.s  |  3 ++
 2 files changed, 45 insertions(+), 43 deletions(-)

diff --git a/isprime/isprime.oph.s b/isprime/isprime.oph.s
index 4066531..262e8f7 100644
--- a/isprime/isprime.oph.s
+++ b/isprime/isprime.oph.s
@@ -40,55 +40,54 @@ isprimex_cli:
 
 max: .byte 0
 
+; accumulator is zero if not prime and nonzero otherwise
 isprimex:
 .scope
-         sec            ; if (number < 2) // equivalent to "number <= 1"
-         txa            ;   // a = x
-         sbc #2         ;   // a -= 2 + 0
-         bmi _false     ;   return False
-
-         sbc #2         ; if (number < 2) // since it was already subtracted, this is equal to "number < 4" or "number <= 3"
-         bmi _end       ;   return True
-
-         txa            ; if (number % 2 == 0)
-         and #1         ;   // number & 0b0001 == 0
-         beq _end       ;   return False
-
-         txa
-         `mod 3         ; if (number % 3 == 0)
-         beq _end       ;   return False
-
-         ldy #6    ; y = 6
-         stx max   ; max = x
-         lsr max   ; max /= 2
-
-_loop:   cpy max   ; if (y >= max)
-         bcs _true ;   return True
-
-         dey       ;     --y
-         txa       ;     a = x
-         `mody     ;     if (a % y == 0)
-         beq _end  ;       return False
-
-         iny       ;     ++y
-         iny       ;     ++y
-         txa       ;     a = x
-         `mody     ;     if (a % y == 0)
-         beq _end  ;       return False
-
-         iny       ;     ++y
-         iny       ;     ++y
-         iny       ;     ++y
-         iny       ;     ++y
-         iny       ;     ++y
-         iny       ;     ++y
-         cpy #5    ; while (y < max)
+         cpx #2     ; if (x < 2)   // x <= 1
+         bcc _false ;   return False
+
+         cpx #4     ; if (x < 4)   // x <= 3
+         bcc _true
+
+         txa        ; a = x
+         and #1     ; if (a % 2 == 0)  // a & 0b0001 == 0
+         beq _end   ;   return False
+
+         txa        ; a = x
+         `mod 3     ; if (a % 3 == 0)
+         beq _end   ;   return False
+
+         ldy #6     ; y = 6
+         stx max    ; max = x
+         lsr max    ; max /= 2
+
+_loop:   cpy max    ; do  if (y >= max)
+         bcs _true  ;       return True
+
+         dey        ;     --y
+         txa        ;     a = x
+         `mody      ;     if (a % y == 0)
+         beq _end   ;       return False
+
+         iny        ;     ++y
+         iny        ;     ++y
+         txa        ;     a = x
+         `mody      ;     if (a % y == 0)
+         beq _end   ;       return False
+
+         iny        ;     ++y
+         iny        ;     ++y
+         iny        ;     ++y
+         iny        ;     ++y
+         iny        ;     ++y
+         iny        ;     ++y
+         cpy #5     ; while (y < max)
          bcc _loop
 
-_true:   lda #1    ; return True
+_true:   lda #1     ; return True
 _end:    rts
 
-_false:  lda #0    ; return False
+_false:  lda #0     ; return False
          rts
 .scend
 
diff --git a/isprime/kernal.oph.s b/isprime/kernal.oph.s
index 5dda4a4..8d4a69e 100644
--- a/isprime/kernal.oph.s
+++ b/isprime/kernal.oph.s
@@ -14,13 +14,16 @@
          tax
 .macend
 
+; print value (byte) at address as a number
 .macro printm
          lda _1
          jsr printa
 .macend
 
+; print register x as a number
 printx:  txa         ; a = x
 
+; print register a as a number
 printa:
 .scope
          cmp #10     ; if (a < 10)
-- 
cgit v1.3.1-23-gd82d