Snail matrix generator

README.md

I made a 133 bytes Snail function such as :

snail(4) =

[[1,  2,  3,  4],
  12, 13, 14, 5],
  11, 16, 15, 6],
  10, 9,  8,  7]]

(and the same logic for snail(N), with N >= 0)

annotated.js

s = function(n,a,d,x,y,c,i){

  // a is the result matrix
  a = [[]];
  
  // d is the direction: right, bottom = 1; left, top = -1
  d = 1;
  
  // c is the counter value.
  c = 0;
  
  // x and y are the coordinates of the number in the matrix
  x = 0;
  y = -1;

  // for n in [n ... 0]
  for(; n; n--){

    // NB: the following two for loops are merged in the minified code
        
    // fill n columns
    for(i = 0; i < n; i++){
      
      y += d;
      a[x][y] = ++c;
    }
    
    // fill n-1 lines 
    for(i = 0; i < n - 1; i++){
      
      x += d;
      if(!a[x]){
        a[x] = [];
      }
      a[x][y] = ++c;
    }

    // change direction
    d = -d;
  }
  
  return a;
}

index.js

s=function(e,c,d,b,f,h,g){c=[[]];d=1;b=h=0;for(f=-1;e;e--){for(g=1;g<2*e;g++)g>e?b+=d:f+=d,c[b]||(c[b]=[]),c[b][f]=++h;d=-d}return c}

LICENSE.txt

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
                    Version 2, December 2004

 Copyright (C) 2011 YOUR_NAME_HERE <YOUR_URL_HERE>

 Everyone is permitted to copy and distribute verbatim or modified
 copies of this license document, and changing it is allowed as long
 as the name is changed.

            DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

  0. You just DO WHAT THE FUCK YOU WANT TO.

package.json

{
  "name": "snail",

  "description": "generates a snail matrix",

  "keywords": [
    "snail",
    "matrix"
  ]
}

test.html

<script>
  s=function(e,c,d,b,f,h,g){c=[[]];d=1;b=h=0;for(f=-1;e;e--){for(g=1;g<2*e;g++)g>e?b+=d:f+=d,c[b]||(c[b]=[]),c[b][f]=++h;d=-d}return c}
  console.log(s(4));
</script>

Save one byte by removing the curly brackets:

function(e,c,d,b,f,h,g){for(c=[[]],d=1,b=h=0,f=-1;e;e--)for(g=1;g<2*e;g++)g>e?b+=d:f+=d,c[b]||(c[b]=[]),c[b][f]=++h;d=-d;return c}

That unfortunately breaks it :/

This one saves 2 bytes by removing brackets (moving d=-d to the last part of the for loop) and moving b=h=0 inside the array definition:

function(e,c,d,b,f,h,g){c=[[b=h=0]];d=1;for(f=-1;e;e--,d=-d)for(g=1;g<2*e;g++)g>e?b+=d:f+=d,c[b]||(c[b]=[]),c[b][f]=++h;return c}

Saving another 2 bytes by changing the check/assignment of c[b]:

function(e,c,d,b,f,h,g){c=[[b=h=0]];d=1;for(f=-1;e;e--,d=-d)for(g=1;g<2*e;g++)g>e?b+=d:f+=d,c[b]=c[b]||[],c[b][f]=++h;return c}

And one more byte (!) by moving to a var-definition instead of placeholder arguments:

function(e){var c=[[]],d=1,b=0,h=0,f,g;for(f=-1;e;e--,d=-d)for(g=1;g<2*e;g++)g>e?b+=d:f+=d,c[b]=c[b]||[],c[b][f]=++h;return c}

-6 bytes:

function(e){for(var c=[[]],d=1,b=0,h=0,f=-1,g;e;e--,d=-d)for(g=1;g<2*e;c[b][f]=++h)g++>e?c[b+=d]=c[b]||[]:f+=d;return c}

I want to ask also, is it necessary c to be [[]], not just [].
The only difference is snail(0) would return [] instead of [[]], but as for me, it is even better.