diff --git a/js/builder/build_encode_decode.js b/js/builder/build_encode_decode.js
index 2c280b7..d67cf64 100644
--- a/js/builder/build_encode_decode.js
+++ b/js/builder/build_encode_decode.js
@@ -4,6 +4,195 @@ let build_powders;
 function getItemNameFromID(id) { return idMap.get(id); }
 function getTomeNameFromID(id) { return tomeIDMap.get(id); }
 
+/*
+ * Populate fields based on url, and calculate build.
+ * TODO: THIS CODE IS GOD AWFUL result of being lazy
+ * fix all the slice() and break into functions or do something about it... its inefficient, ugly and error prone
+ */
+async function parse_hash(url_tag) {
+    const default_load_promises = [ load_atree_data(wynn_version_names[WYNN_VERSION_LATEST]),
+                                    load_init(), load_ing_init(), load_tome_init() ];
+    if (!url_tag) {
+        await Promise.all(default_load_promises);
+        return;
+    }
+    //default values
+    let equipment = [null, null, null, null, null, null, null, null, null];
+    let tomes = [null, null, null, null, null, null, null];
+    let powdering = ["", "", "", "", ""];
+    let info = url_tag.split("_");
+    let version = info[0];
+    let save_skp = false;
+    let skillpoints = [0, 0, 0, 0, 0];
+    let level = 106;
+
+    let version_number = parseInt(version);
+    let data_str = info[1];
+    if (version_number >= 8) {
+        // parse query parameters
+        // https://stackoverflow.com/questions/901115/how-can-i-get-query-string-values-in-javascript
+        const url_params = new URLSearchParams(window.location.search);
+        const version_id = url_params.get('v');
+        wynn_version_id = parseInt(version_id);
+        if (isNaN(wynn_version_id) || wynn_version_id > WYNN_VERSION_LATEST || wynn_version_id < 0) {
+            // TODO: maybe make the NAN try to use the human readable version?
+            // NOTE: Failing silently... do we want to raise a loud error?
+            console.log("Explicit version not found or invalid, using latest version");
+            wynn_version_id = WYNN_VERSION_LATEST;
+        }
+        else {
+            console.log(`Build link for wynn version ${wynn_version_id} (${wynn_version_names[wynn_version_id]})`);
+        }
+    }
+    else {
+        // Change the default to oldest. (A time before v8)
+        wynn_version_id = 0;
+    }
+
+    // the deal with this is because old versions should default to 0 (oldest wynn item version), and v8+ defaults to latest.
+    // its ugly... but i think this is the behavior we want...
+    if (wynn_version_id != WYNN_VERSION_LATEST) {
+        // force reload item database and such.
+        // TODO MUST: display a warning showing older version!
+        const msg = 'This build was created in an older version of wynncraft '
+                    + `(${wynn_version_names[wynn_version_id]} < ${wynn_version_names[WYNN_VERSION_LATEST]}). `
+                    + 'Would you like to update to the latest version? Updating may break the build and ability tree.';
+
+        if (confirm(msg)) {
+            wynn_version_id = WYNN_VERSION_LATEST;
+        }
+        else {
+            version_name = wynn_version_names[wynn_version_id];
+            const load_promises = [ load_atree_data(version_name),
+                                    load_old_version(version_name),
+                                    load_ings_old_version(version_name),
+                                    load_tome_old_version(version_name) ];
+            console.log("Loading old version data...", version_name)
+            await Promise.all(load_promises);
+        }
+    }
+    if (wynn_version_id == WYNN_VERSION_LATEST) {
+        await Promise.all(default_load_promises);
+    }
+
+    //equipment (items)
+    // TODO: use filters
+    if (version_number < 4) {
+        let equipments = info[1];
+        for (let i = 0; i < 9; ++i ) {
+            let equipment_str = equipments.slice(i*3,i*3+3);
+            equipment[i] = getItemNameFromID(Base64.toInt(equipment_str));
+        }
+        data_str = equipments.slice(27);
+    }
+    else if (version_number == 4) { 
+        let info_str = data_str;
+        let start_idx = 0;
+        for (let i = 0; i < 9; ++i ) {
+            if (info_str.charAt(start_idx) === "-") {
+                equipment[i] = "CR-"+info_str.slice(start_idx+1, start_idx+18);
+                start_idx += 18;
+            }
+            else {
+                let equipment_str = info_str.slice(start_idx, start_idx+3);
+                equipment[i] = getItemNameFromID(Base64.toInt(equipment_str));
+                start_idx += 3;
+            }
+        }
+        data_str = info_str.slice(start_idx);
+    }
+    else if (version_number <= 8) {
+        let info_str = data_str;
+        let start_idx = 0;
+        for (let i = 0; i < 9; ++i ) {
+            if (info_str.slice(start_idx,start_idx+3) === "CR-") {
+                equipment[i] = info_str.slice(start_idx, start_idx+20);
+                start_idx += 20;
+            } else if (info_str.slice(start_idx+3,start_idx+6) === "CI-") {
+                let len = Base64.toInt(info_str.slice(start_idx,start_idx+3));
+                equipment[i] = info_str.slice(start_idx+3,start_idx+3+len);
+                start_idx += (3+len);
+            } else {
+                let equipment_str = info_str.slice(start_idx, start_idx+3);
+                equipment[i] = getItemNameFromID(Base64.toInt(equipment_str));
+                start_idx += 3;
+            }
+        }
+        data_str = info_str.slice(start_idx);
+    }
+    //constant in all versions
+    for (let i in equipment) {
+        setValue(equipment_inputs[i], equipment[i]);
+    }
+
+    //level, skill point assignments, and powdering
+    if (version_number == 1) {
+        let powder_info = data_str;
+        let res = parsePowdering(powder_info);
+        powdering = res[0];
+    } else if (version_number == 2) {
+        save_skp = true;
+        let skillpoint_info = data_str.slice(0, 10);
+        for (let i = 0; i < 5; ++i ) {
+            skillpoints[i] = Base64.toIntSigned(skillpoint_info.slice(i*2,i*2+2));
+        }
+
+        let powder_info = data_str.slice(10);
+        let res = parsePowdering(powder_info);
+        powdering = res[0];
+    } else if (version_number <= 8){
+        level = Base64.toInt(data_str.slice(10,12));
+        setValue("level-choice",level);
+        save_skp = true;
+        let skillpoint_info = data_str.slice(0, 10);
+        for (let i = 0; i < 5; ++i ) {
+            skillpoints[i] = Base64.toIntSigned(skillpoint_info.slice(i*2,i*2+2));
+        }
+
+        let powder_info = data_str.slice(12);
+
+        let res = parsePowdering(powder_info);
+        powdering = res[0];
+        data_str = res[1];
+    }
+    // Tomes.
+    if (version_number >= 6) {
+        //tome values do not appear in anything before v6.
+        if (version_number < 8) {
+            for (let i in tomes) {
+                let tome_str = data_str.charAt(i);
+                let tome_name = getTomeNameFromID(Base64.toInt(tome_str));
+                setValue(tomeInputs[i], tome_name);
+            }
+            data_str = data_str.slice(7);
+        }
+        else {
+            // 2chr tome encoding to allow for more tomes.
+            for (let i in tomes) {
+                let tome_str = data_str.slice(2*i, 2*i+2);
+                let tome_name = getTomeNameFromID(Base64.toInt(tome_str));
+                setValue(tomeInputs[i], tome_name);
+            }
+            data_str = data_str.slice(14);
+        }
+    }
+
+    if (version_number >= 7) {
+        // ugly af. only works since its the last thing. will be fixed with binary decode
+        atree_data = new BitVector(data_str);
+    }
+    else {
+        atree_data = null;
+    }
+
+    for (let i in powder_inputs) {
+        setValue(powder_inputs[i], powdering[i]);
+    }
+    for (let i in skillpoints) {
+        setValue(skp_order[i] + "-skp", skillpoints[i]);
+    }
+}
+
 function parsePowdering(powder_info) {
     // TODO: Make this run in linear instead of quadratic time... ew
     let powdering = [];
diff --git a/js/utils.js b/js/utils.js
index 7fd8c8b..c432812 100644
--- a/js/utils.js
+++ b/js/utils.js
@@ -172,7 +172,13 @@ Base64 = (function () {
                 }
             }
         } else if (typeof data === "number") {
-            if (typeof length === "undefined")
+            if (typeof length === "undefined") {
+                if (data == 0) {
+                    length = 0;
+                } else {
+                    length = Math.ceil(Math.log(data) / Math.log(2));
+                }
+            }
             if (length < 0) {
                 throw new RangeError("BitVector must have nonnegative length.");
             }
@@ -333,13 +339,9 @@ Base64 = (function () {
         let new_length = this.length + length;
         if (this.bits.length * this.bits.BYTES_PER_ELEMENT * 8 < new_length) {
             //resize the internal repr by a factor of 2 before recursive calling
-            let bit_vec = [];
-            for (const int of this.bits) {
-                bit_vec.push(int);
-            }
-            //effectively double size - TODO 1-line this
-            for (const int of this.bits) {
-                bit_vec.push(0);
+            let bit_vec = Array(2 * this.bits.length).fill(0);
+            for (let i = 0; i < this.bits.length; i++) {
+                bit_vec[i] = this.bits[i];
             }
 
             this.bits = new Uint32Array(bit_vec);
@@ -403,6 +405,18 @@ Base64 = (function () {
     }
 };
 
+function test_bv() {
+    //empty array
+    let bv = new BitVector(0);
+    bv.append(10, 4);
+    console.log(bv);
+
+    bv = new BitVector(0);   
+    bv.append(10, 5);
+    console.log(bv);
+
+}
+
 
 /*
     Turns a raw stat and a % stat into a final stat on the basis that - raw and >= 100% becomes 0 and + raw and <=-100% becomes negative.
@@ -1039,4 +1053,6 @@ if (screen.width < 992) {
         }
         scrollPos = document.documentElement.scrollTop;
     });
-}
\ No newline at end of file
+}
+
+test_bv();
\ No newline at end of file