From ec3b438f40170b63cf02ff46ad87936347027b78 Mon Sep 17 00:00:00 2001
From: Joseph Montanaro <jfmonty2@gmail.com>
Date: Fri, 6 Dec 2024 20:39:16 -0500
Subject: [PATCH] 2024 day 3 part 2

---
 2024/03.fs | 82 +++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 54 insertions(+), 28 deletions(-)

diff --git a/2024/03.fs b/2024/03.fs
index 7a6ed62..26a57f2 100644
--- a/2024/03.fs
+++ b/2024/03.fs
@@ -1,16 +1,11 @@
-create data 20000 allot \ create a 20K buffer
-variable fileid \ create a variable `fileid`
-s" data/03.txt" r/o open-file \ open data file
-drop \ drop the top value from the stack, it's just a status code and we aren't going to bother handling errors
-fileid ! \ save the file id to the variable
+: load-data ( addr1 u1 -- addr2 u2 )
+    20000 allocate drop   \ allocate a 20k buffer, drop the status code
+    dup 2swap             \ duplicate the buffer addr and stick both copies under the addr/length of filename
+    r/o open-file drop    \ open file, drop the status code
+    20000 swap            \ stick the number of bytes to be read in between the buffer addr and file id
+    read-file drop        \ read the file, drop the status code
+;
 
-variable data-len
-data 20000 fileid @ read-file
-drop
-data-len !
-
-: data-str ( -- addr u )
-    data data-len @ ;
 
 : chop-prefix ( addr u u2 -- addr2 u2 )
     \ chop the first `u2` bytes off the beginning of the string at `addr u`
@@ -21,9 +16,11 @@ data-len !
     swap    \ put them back in the right order
 ;
 
+
 require regexp.fs
 
 : mul-instr ( addr u -- flag )
+    \ match a string of the form `mul(x,y)` where x and y are integers and capture those integers
     (( =" mul(" \( {++ \d ++} \) ` , \( {++ \d ++} \) ` ) )) ;
 
 
@@ -38,24 +35,53 @@ require regexp.fs
     then
 ;
 
-variable result
+
+variable result            \ initialize `result` with 0
 0 result !
 
-: sum-mul-instrs ( addr u -- u2 )
-    begin                  \ start looping
-        s" mul(" search    \ search for the string "mul("
-        if                 \ if successful, top 2 values on stack will be start address of "mul(" and remainder of original string
-            2dup           \ duplicate address and remaining length of string
-            get-product    \ pass those to get-product above
-            result @ +     \ load `result` and add to product
-            result !       \ store this new value back in `result`
-            4 chop-prefix  \ bump the start of the string by 4 characters
-        else               \ if not successful, we have finished scanning through the string
-            2drop          \ dump the string address and length
-            result @ exit  \ put the result on top of the stack and return to caller
-        then
-    again
+variable enabled
+-1 enabled !               \ idiomatically -1 is "true" (really anything other than 0 is true)
+
+: handle-mul ( addr u -- )
+    get-product    \ pass those to get-product above
+    result @ +     \ load `result` and add to product
+    result !       \ store this new value back in `result`
 ;
 
-data-str sum-mul-instrs .
+: sum-mul-instrs ( addr u -- u2 )
+    \ we want to loop from addr to (addr + u - 8), because 8 is the min length of a valid mul(x,y) instruction
+    \ we also want to have addr + u on the top of the stack when we enter the loop,
+    \ so that we can use that to compute the remaining length of the string from our current address
+
+    over +    \ copy addr to top of stack and add to length
+    dup 8 -   \ duplicate, then subtract 8 from the top value
+    rot       \ move original addr to top of stack
+    ( stack at this point: [ addr + u, addr + u - 8, addr ] )
+    ( i.e. [ end-of-string, loop-limit, loop-start ] )
+
+    do                      \ start looping
+        I 4 s" do()" str=   \ compare the length-4 substring starting at I to the string "do()"
+        if                  \ if valid do() instruction,
+            -1 enabled !    \ set enabled=true
+        then
+
+        I 7 s" don't()" str=   \ compare length-7 substring to "don't()"
+        if                     \ if valid don't() instruction,
+            0 enabled !        \ set enabled=false
+        then
+
+        I 4 s" mul(" str=       \ compare length-4 substring to "mul("
+        enabled @ and           \ combine with current value of `enabled`
+        if                      \ if a candidate for `mul(x,y)` instruction, and enabled=true, then
+            dup I -             \ subtract current string pointer from end-of-string pointer to get length of remaining string
+            I swap handle-mul   \ put current pointer onto stack again, swap so stack is ( addr len), and handle
+        then
+    loop
+
+    drop       \ get rid of end-of-string pointer
+    result @   \ return value of result
+;
+
+s" data/03.txt" load-data
+sum-mul-instrs .
 bye