2 files changed, 21 insertions, 13 deletions
diff --git a/src/genome/genome.js b/src/genome/genome.js
index 3445fe9..71e18c1 100644
--- a/src/genome/genome.js
+++ b/src/genome/genome.js
@@ -9,7 +9,8 @@ export const mutation_type = Object.freeze({
 });
 
 
-function positive(x) {
+// clamp a number in the range [0, infinity)
+function nonneg(x) {
   if (x < 0) { 
     return 0; 
   } else {
@@ -18,6 +19,7 @@ function positive(x) {
 }
 
 
+// mutate a gene
 export function mutate(gene, type, value) {
   const [ source, sink, weight ] = gene;
 
@@ -27,14 +29,14 @@ export function mutate(gene, type, value) {
 
     case mutation_type.source:
       if (value <= 0.5) {
-        return [ positive(source-1), sink, weight ];
+        return [ nonneg(source-1), sink, weight ];
       } else {
         return [ source+1, sink, weight ];
       }
 
     case mutation_type.sink:
       if (value <= 0.5) {
-        return [ source, positive(sink-1), weight ];
+        return [ source, nonneg(sink-1), weight ];
       } else {
         return [ source, sink+1, weight ];
       }
@@ -49,7 +51,8 @@ export function mutate(gene, type, value) {
 }
 
 
-export function is_valid(num_input, num_output, genome) {
+// check if a given genome is valid and compute its size
+export function get_size(num_input, num_output, genome) {
   const [ max_index, max_weight ] = genome.reduce(
     ([max_index, max_weight ], [ source, sink, weight]) => [
       Math.max(max_index, source, sink),
@@ -59,12 +62,12 @@ export function is_valid(num_input, num_output, genome) {
   );
 
   if (max_index < num_input + num_output - 1) {
-    return false;
+    return -1;
   }
   else if (max_weight > 4.0) {
-    return false;
+    return -1;
   }
   else {
-    return true;
+    return max_index + 1;
   }
 }
diff --git a/src/genome/genome.test.js b/src/genome/genome.test.js
index f50531b..0ad8d80 100644
--- a/src/genome/genome.test.js
+++ b/src/genome/genome.test.js
@@ -2,7 +2,7 @@
 
 import { 
   mutation_type, mutate,
-  is_valid,
+  get_size,
 } from './genome';
 
 
@@ -23,9 +23,14 @@ test('basic gene mutations', () => {
 });
 
 
-test('genome validation', () => {
-  expect(is_valid(0, 0, [ [ 0, 0, 1.0 ] ])).toBe(true);
-  expect(is_valid(2, 1, [ [ 0, 2, 1 ] ])).toBe(true);
-  expect(is_valid(2, 1, [ [ 0, 1, 1 ] ])).toBe(false);
-  expect(is_valid(2, 1, [ [ 0, 2, 5 ] ])).toBe(false);
+test('genome validation and size', () => {
+  expect(get_size(0, 0, [ [ 0, 0, 1.0 ] ])).toBe(1);
+  expect(get_size(2, 1, [ [ 0, 2, 1 ] ])).toBe(3);
+  expect(get_size(2, 1, [ [ 0, 1, 1 ] ])).toBe(-1);
+  expect(get_size(2, 1, [ [ 0, 2, 5 ] ])).toBe(-1);
+});
+
+
+test('parse a genome into a neural net', () => {
+  
 });