Reword ndxFn assignment

dingosky · dingosky · commit 87d626136be0 · 2017-08-10T09:45:47.000-07:00
diff --git a/lib/charSet.js b/lib/charSet.js
@@ -1,14 +1,16 @@
 import lcm from './lcm'
 
 class CharSet {
-  constructor(chars, ndxFn) {
+  constructor(chars) {
+    let bitsPerByte = 8
+    
     this.chars = chars
-    this.ndxFn = ndxFn
     this.bitsPerChar = Math.floor(Math.log2(chars.length))
     if (this.bitsPerChar != Math.log2(chars.length)) {
       throw new Error('EntropyString only supports CharSets with a power of 2 characters')
     }
-    this.charsPerChunk = lcm(this.bitsPerChar, 8) / this.bitsPerChar
+    this.ndxFn = this._ndxFn(this.bitsPerChar)
+    this.charsPerChunk = lcm(this.bitsPerChar, bitsPerByte) / this.bitsPerChar
   }
 
   use(chars) {
@@ -28,63 +30,45 @@ class CharSet {
     }
     this.chars = chars
   }
-}
-
-const _ndx64 = (chunk, slice, bytes) => {
-  return _ndxGen(chunk, slice, bytes, 6)
-}
-
-const _ndx32 = (chunk, slice, bytes) => {
-  return _ndxGen(chunk, slice, bytes, 5)
-}
 
-const _ndx16 = (chunk, slice, bytes) => {
-  return _ndxDiv(chunk, slice, bytes, 4)
-}
-
-const _ndx8 = (chunk, slice, bytes) => {
-  return _ndxGen(chunk, slice, bytes, 3)
-}
-
-const _ndx4 = (chunk, slice, bytes) => {
-  return _ndxDiv(chunk, slice, bytes, 2)
-}
-
-const _ndx2 = (chunk, slice, bytes) => {
-  return _ndxDiv(chunk, slice, bytes, 1)
-}
-
-const _ndxGen = (chunk, slice, bytes, bitsPerChar) => {
-  let bitsPerByte = 8
-  let slicesPerChunk = lcm(bitsPerChar, bitsPerByte) / bitsPerByte
-  let bNum = chunk * slicesPerChunk
+  _ndxFn(bitsPerChar) {
+    let bitsPerByte = 8
+    
+    if (lcm(bitsPerChar, bitsPerByte) === bitsPerByte) {
+      return function(chunk, slice, bytes) {
+        let lShift = bitsPerChar
+        let rShift = bitsPerByte - bitsPerChar
+        return ((bytes[chunk]<<(lShift*slice))&0xff)>>rShift
+      }
+    }
+    else {
+      return function(chunk, slice, bytes) {
+        let slicesPerChunk = lcm(bitsPerChar, bitsPerByte) / bitsPerByte
+        let bNum = chunk * slicesPerChunk
 
-  let rShift = bitsPerByte - bitsPerChar
-  let lOffset = Math.floor((slice*bitsPerChar)/bitsPerByte)
-  let lShift = (slice*bitsPerChar) % bitsPerByte
+        let rShift = bitsPerByte - bitsPerChar
+        let lOffset = Math.floor((slice*bitsPerChar)/bitsPerByte)
+        let lShift = (slice*bitsPerChar) % bitsPerByte
 
-  let ndx = ((bytes[bNum+lOffset]<<lShift)&0xff)>>rShift
+        let ndx = ((bytes[bNum+lOffset]<<lShift)&0xff)>>rShift
 
-  let rOffset = Math.ceil((slice*bitsPerChar)/bitsPerByte)
-  let rShiftIt = ((rOffset+1)*bitsPerByte - (slice+1)*bitsPerChar) % bitsPerByte
-  if (rShift < rShiftIt) {
-    ndx += bytes[bNum+rOffset]>>rShiftIt
+        let rOffset = Math.ceil((slice*bitsPerChar)/bitsPerByte)
+        let rShiftIt = ((rOffset+1)*bitsPerByte - (slice+1)*bitsPerChar) % bitsPerByte
+        if (rShift < rShiftIt) {
+          ndx += bytes[bNum+rOffset]>>rShiftIt
+        }
+        return ndx
+      }      
+    }
   }
-  return ndx
-}
-
-const _ndxDiv = (chunk, slice, bytes, bitsPerChar) => {
-  let lShift = bitsPerChar
-  let rShift = 8 - bitsPerChar
-  return ((bytes[chunk]<<(lShift*slice))&0xff)>>rShift
 }
 
 export default {
-  charSet64: new CharSet('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_', _ndx64),
-  charSet32: new CharSet('2346789bdfghjmnpqrtBDFGHJLMNPQRT', _ndx32),
-  charSet16: new CharSet('0123456789abcdef', _ndx16),
-  charSet8:  new CharSet('01234567', _ndx8),
-  charSet4:  new CharSet('ATCG', _ndx4),
-  charSet2:  new CharSet('01', _ndx2),
+  charSet64: new CharSet('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_'),
+  charSet32: new CharSet('2346789bdfghjmnpqrtBDFGHJLMNPQRT'),
+  charSet16: new CharSet('0123456789abcdef'),
+  charSet8:  new CharSet('01234567'),
+  charSet4:  new CharSet('ATCG'),
+  charSet2:  new CharSet('01'),
   isValid:   (charSet) => charSet instanceof CharSet
 }
