diff --git a/src/array.asm b/src/array.asm
index c90ba38..30b4c2c 100644
--- a/src/array.asm
+++ b/src/array.asm
@@ -7,6 +7,7 @@
 ; r5 - Predicate context
 ; Result:
 ; r1 - The index of the first element matching the provided predicate function (or -1 if not found)
+; flags - 0, if the element does not exist in the array. 1 if the element does exist.
 ; Clobbers: r2, r3, r4, r5, r6, + what the predicate clobbers
 ; Info:
 ; The predicate function should follow the stdlib calling convention
@@ -74,4 +75,6 @@ pub find_index:
         pop r10
         pop r11
         pop r12
+        lsr flags, r1, 31
+        xor flags, flags, 1
         jmp r13 ; Return
diff --git a/src/hashset.asm b/src/hashset.asm
new file mode 100644
index 0000000..93d2be0
--- /dev/null
+++ b/src/hashset.asm
@@ -0,0 +1,227 @@
+;struct Allocator {
+;   alloc: (U32) -> ptr
+;   realloc: (ptr, U32) -> ptr
+;   free: (ptr) -> ()
+;}
+
+;struct HashSet {
+;   buckets: U32
+;   alloc_ptr: *Allocator
+;   hash_ptr: *(Item) -> U32
+;   hash_context: U32
+;   eq_ptr: *(Item, Item) -> Bool
+;   eq_context: U32
+;   data_ptr: *HashBucket
+;}
+
+;struct HashBucket {
+;   hash0: U32
+;   item0: Item
+;   hash1: U32
+;   item1: Item
+;   hash2: U32
+;   item2: Item
+;   hash3: U32
+;   item3: Item
+;}
+
+; Checks if the hashset contains a specified element
+; Arguments:
+; r1 - The element to check
+; r2 - The pointer to the hashset
+; Result:
+; r1 - 0, if the element does not exist in the hashset. 1 if the element does exist.
+; r2 - The pointer to the hashset
+; flags - 0, if the element does not exist in the hashset. 1 if the element does exist.
+pub contains:
+    push r13
+    push r8
+    push r9
+    push r10
+    push r11
+    push r12
+    
+    mov r8, r1
+    mov r9, r2
+    
+    add r3, r2, 8
+    load_32 r3, [r3] ; Loading the hash pointer
+    add r2, r2, 12
+    load_32 r2, [r2] ; Loading the hash context
+
+    counter r13
+    add r13, r13, 12
+    jmp r3 ; Calling the hash function with element in r1, context in r2
+
+    cmp r1, rz
+    jne contains_skip_one
+    add r1, r1, 1 ; If hash is zero, we add 1. That way hash being 0 means the item does not exist at a position
+    contains_skip_one:
+
+    mov r12, r1
+
+    add r10, r9, 16
+    load_32 r10, [r10] ; Loading the eq pointer
+    add r11, r9, 20
+    load_32 r11, [r11] ; Loading the eq context
+
+    ; We have:
+    ; item in r8
+    ; bucket pointer in r9
+    ; eq pointer in r10
+    ; eq context in r11
+    ; item hash in r12
+
+    load_32 r2, [r9] ; Loading buckets
+    sub r2, r2, 1
+    and r2, r1, r2 ; bucket_index = hash & (buckets - 1)
+
+    add r3, r9, 24
+    load_32 r3, [r3] ; Loading data pointer
+    lsl r2, r2, 5 ; Each bucket is 32 bytes
+    push r9
+    add r9, r2, r3 ; Pointer to bucket
+
+        load_32 r3, [r9] ; First hash
+        cmp r3, rz
+        je contains_notfourth ; If hash is zero, no items left to check
+        cmp r12, r3
+        jne contains_notfirst
+        ; First item hash passed - checking equality
+        mov r13, contains_notfirst
+        jmp contains_eqcheck
+
+    contains_notfirst:
+        add r9, r9, 8
+        load_32 r3, [r9] ; Second hash
+        cmp r3, rz
+        je contains_notfourth ; If hash is zero, no items left to check
+        cmp r12, r3
+        jne contains_notsecond
+        ; Second item hash passed - checking equality
+        mov r13, contains_notsecond
+        jmp contains_eqcheck
+
+    contains_notsecond:
+        add r9, r9, 8
+        load_32 r3, [r9] ; Third hash
+        cmp r3, rz
+        je contains_notfourth ; If hash is zero, no items left to check
+        cmp r12, r3
+        jne contains_notthird
+        ; Third item hash passed - checking equality
+        mov r13, contains_notthird
+        jmp contains_eqcheck
+
+    contains_notthird:
+        add r9, r9, 8
+        load_32 r3, [r9] ; Fourth hash
+        cmp r3, rz
+        je contains_notfourth ; If hash is zero, no items left to check
+        cmp r12, r3
+        jne contains_notfourth
+        ; Fourth item hash passed - checking equality
+        mov r13, contains_notfourth
+        jmp contains_eqcheck
+
+    contains_notfourth:
+        mov r1, 0
+    contains_finish:
+        pop r2
+        pop r12
+        pop r11
+        pop r10
+        pop r9
+        pop r8
+        pop r13
+        mov flags, r1
+        jmp r13
+    
+    contains_found:
+        mov r1, 1
+        jmp contains_finish
+
+    contains_eqcheck:
+        add r3, r9, 4
+        load_32 r2, [r3]
+        mov r3, r11
+        mov r1, r8
+        jmp r10 ; Calling eq check
+        cmp r1, zr
+        jne contains_found
+        jmp r13
+
+; Creates a hashset for the specified allocator, hash function and equality function
+; Arguments:
+; r1 - The pointer to the allocator
+; r2 - The hash function
+; r3 - The hash function context
+; r4 - The equality function
+; r5 - The equality function context
+; Result:
+; r1 - The pointer to the hashset structure
+; Info:
+; The hash function should follow the stdlib calling convention
+; The hash function receives one argument (the value of the item) and should return an integer which remains the same for the lifetime of the value.
+; The equality function should follow the stdlib calling convention
+; The equality function receives two arguments (the value of the two items) and should return either a zero (when the items are not equal) or any other value (if they are equal).
+pub new:
+    ; First let's free up all the registers
+    push r8
+    push r9
+    push r10
+    push r11
+    push r12
+    push r13 ; We will be calling alloc
+
+    mov r8, r1
+    mov r9, r2
+    mov r10, r3
+    mov r11, r4
+    mov r12, r5
+
+    load_32 r5, [r8] ; Loading the alloc function address
+    mov r1, 28
+    counter r13
+    add r13, r13, 12
+    jmp r5 ; allocating the space for the hashset struct itself
+
+    ; Now r1 has the pointer to memory, r2-r7 are clobbered
+
+    mov r2, 8
+    store_32 [r1], r2 ; initial capacity at 8 buckets
+
+    add r1, r1, 4
+    store_32 [r1], r8 ; allocator pointer is in r8
+
+    add r1, r1, 4
+    store_32 [r1], r9 ; hash pointer is in r9
+
+    add r1, r1, 4
+    store_32 [r1], r10 ; hash context is in r10
+
+    add r1, r1, 4
+    store_32 [r1], r11 ; eq pointer is in r11
+
+    add r1, r1, 4
+    store_32 [r1], r12 ; eq context is in r12
+
+    add r12, r1, 4 ; Now r12 is hashset pointer at data_ptr
+
+    load_32 r5, [r8] ; Loading the alloc function address
+    mov r1, 256 ; 8 buckets * 4 items * 8 bytes per each
+    counter r13
+    add r13, r13, 12
+    jmp r5 ; allocating the space for the data
+
+    store_32 [r2], r1 ; data pointer saved
+
+    sub r1, r12, 24 ; Getting the pointer to start of the hashset
+
+    pop r13 ; Everything's set up, return
+    pop r12
+    pop r11
+    pop r10
+    pop r9
+    pop r8
+    jmp r13
\ No newline at end of file