From 8a463207ae72e0808bb3fd382866f9dcbeaf2bc4 Mon Sep 17 00:00:00 2001
From: Michal Isalski <Michal.Isalski@NeoviciAB.onmicrosoft.com>
Date: Mon, 31 Aug 2026 13:44:07 +0200
Subject: [PATCH] Added find_index array function

---
 array.asm | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/array.asm b/array.asm
index 13dfc4b..798d8d8 100644
--- a/array.asm
+++ b/array.asm
@@ -5,13 +5,13 @@
 ; r4 - The predicate
 ; r5 - Predicate context
 ; The predicate function should follow the stdlib calling convention
-; The predicate receives two arguments (the value and the predicate context) and should return either a zero when the value is not the one we search for
+;  and receive one argument and return either a zero when the value is not the one we search for
 ; , or any other result if it is the searched-for item.
 pub find_index:
     push r12 ; We will store the predicate pointer here
     push r11 ; We will store the current pointer here
     push r10 ; We will store the stride here
-    push r9 ; We will store the final address here
+    push r9 ; We will store the bytes left here
     push r8 ; We will store the mask here
     push r1 ; We need the array pointer to calculate the item index
 
@@ -19,15 +19,14 @@ pub find_index:
     mov r11, r1
     mov r10, r3
     mov r9, r2
-    lsr r6, r3, 1 ; We turn the stride into a byte shift
-    lsl r9, r9, r6 ; We calculate bytes left
-    add r9, r9, r1 ; We add the start address to get the final address
+    lsl r9, r9, r3
 
     push r13 ; We save up the return address because we will provide our own to the predicate
     counter r13
-    add r13, r13, 52 ; Point to just after the predicate call - we can set this up now so we don't waste loop cycles
+    add r13, r13, 40 ; Point to just after the predicate call - we can set this up now so we don't waste loop cycles
 
-    nand r8, zr, zr ; We create a mask of 0xFFFFFFFF
+    mov r8, 0
+    not r8, r8 ; We create a mask of 0xFFFFFFFF
     mov r6, 4
     sub r6, r6, r3 ; We create a "negative stride", e.g. 4 -> 0, 2 -> 2, 1 -> 3
     lsl r6, r6, 3
@@ -43,17 +42,19 @@ pub find_index:
         load_32 r2, [sp] ; We load the predicate context into r2
         jmp r12 ; We call the predicate
         cmp r1, zr
-        jne find_index_found_item ; If we found the item, we jump out
+        jneq find_index_found_item ; If we found the item, we jump out
         ; If we didn't, move to next item
         add r11, r11, r10 ; We add the stride to the pointer
-        cmp r11, r9 ; We compare with the final address
-        je find_index_not_found ; If we reached the end we're done
+        sub r9, r9, r10 ; We decrease bytes left
+        cmp r9, zr
+        jeq find_index_not_found ; If we reached the end we're done
         jmp find_index_loop
     
     find_index_not_found:
         add sp, sp, 4 ; The predicate context is not useful
         pop r13 ; We get our return address
-        nand r1, zr, zr ; We put -1 in r1
+        mov r1, 0
+        not r1, r1 ; We put -1 in r1
         add sp, sp, 4 ; The old array pointer are not useful
         jmp find_index_postamble
     
@@ -72,3 +73,4 @@ pub find_index:
         pop r11
         pop r12
         jmp r13 ; Return
+