From bc024e3d3db856b75a637837136064d3b3558518 Mon Sep 17 00:00:00 2001
From: Alan Sikora <alansikora@gmail.com>
Date: Thu, 27 Sep 2018 12:34:23 -0300
Subject: [PATCH] Added the possibility of reading little endian bits

---
 lib/binary_parser.js | 75 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 70 insertions(+), 5 deletions(-)

diff --git a/lib/binary_parser.js b/lib/binary_parser.js
index 12ece7ee..1fdccc56 100644
--- a/lib/binary_parser.js
+++ b/lib/binary_parser.js
@@ -29,7 +29,8 @@ var SPECIAL_TYPES = {
   Skip: null,
   Choice: null,
   Nest: null,
-  Bit: null
+  Bit: null,
+  Bitle: null,
 };
 
 var aliasRegistry = {};
@@ -100,6 +101,14 @@ BIT_RANGE.forEach(function(i) {
     options.length = i;
     return this.setNextParser("bit", varName, options);
   };
+  
+  Parser.prototype["bitle" + i.toString()] = function(varName, options) {
+    if (!options) {
+      options = {};
+    }
+    options.length = i;
+    return this.setNextParser("bitle", varName, options);
+  };
 });
 
 Parser.prototype.namely = function(alias) {
@@ -487,17 +496,17 @@ Parser.prototype.generateBit = function(ctx) {
       ctx.pushCode("var {0} = buffer.readUInt8(offset);", val);
       sum = 8;
     } else if (sum <= 16) {
-      ctx.pushCode("var {0} = buffer.readUInt16BE(offset);", val);
+      ctx.pushCode(`var {0} = buffer.readUInt16BE(offset);`, val);
       sum = 16;
     } else if (sum <= 24) {
       var val1 = ctx.generateTmpVariable();
       var val2 = ctx.generateTmpVariable();
-      ctx.pushCode("var {0} = buffer.readUInt16BE(offset);", val1);
+      ctx.pushCode(`var {0} = buffer.readUInt16BE(offset);`, val1);
       ctx.pushCode("var {0} = buffer.readUInt8(offset + 2);", val2);
       ctx.pushCode("var {2} = ({0} << 8) | {1};", val1, val2, val);
       sum = 24;
     } else if (sum <= 32) {
-      ctx.pushCode("var {0} = buffer.readUInt32BE(offset);", val);
+      ctx.pushCode(`var {0} = buffer.readUInt32BE(offset);`, val);
       sum = 32;
     } else {
       throw new Error(
@@ -523,6 +532,62 @@ Parser.prototype.generateBit = function(ctx) {
   }
 };
 
+Parser.prototype.generateBitle = function(ctx) {
+  // TODO find better method to handle nested bit fields
+  var parser = JSON.parse(JSON.stringify(this));
+  parser.varName = ctx.generateVariable(parser.varName);
+  ctx.bitFields.push(parser);
+
+  if (
+    !this.next ||
+    (this.next && ["Bitle", "Nest"].indexOf(this.next.type) < 0)
+  ) {
+    var sum = 0;
+    ctx.bitFields.forEach(function(parser) {
+      sum += parser.options.length;
+    });
+
+    var val = ctx.generateTmpVariable();
+
+    if (sum <= 8) {
+      ctx.pushCode("var {0} = buffer.readUInt8(offset);", val);
+      sum = 8;
+    } else if (sum <= 16) {
+      ctx.pushCode(`var {0} = buffer.readUInt16LE(offset);`, val);
+      sum = 16;
+    } else if (sum <= 24) {
+      var val1 = ctx.generateTmpVariable();
+      var val2 = ctx.generateTmpVariable();
+      ctx.pushCode(`var {0} = buffer.readUInt16LE(offset);`, val1);
+      ctx.pushCode("var {0} = buffer.readUInt8(offset + 2);", val2);
+      ctx.pushCode("var {2} = ({0} << 8) | {1};", val1, val2, val);
+      sum = 24;
+    } else if (sum <= 32) {
+      ctx.pushCode(`var {0} = buffer.readUInt32LE(offset);`, val);
+      sum = 32;
+    } else {
+      throw new Error(
+        "Currently, bit field sequence longer than 4-bytes is not supported."
+      );
+    }
+    ctx.pushCode("offset += {0};", sum / 8);
+
+    var bitOffset = 0;
+    ctx.bitFields.forEach(function(parser) {
+      ctx.pushCode(
+        "{0} = {1} >> {2} & {3};",
+        parser.varName,
+        val,
+        bitOffset,
+        (1 << parser.options.length) - 1
+      );
+      bitOffset += parser.options.length;
+    });
+
+    ctx.bitFields = [];
+  }
+};
+
 Parser.prototype.generateSkip = function(ctx) {
   var length = ctx.generateOption(this.options.length);
   ctx.pushCode("offset += {0};", length);
@@ -739,7 +804,7 @@ Parser.prototype.generateFormatter = function(ctx, varName, formatter) {
 };
 
 Parser.prototype.isInteger = function() {
-  return !!this.type.match(/U?Int[8|16|32][BE|LE]?|Bit\d+/);
+  return !!this.type.match(/U?Int[8|16|32][BE|LE]?|Bit\d+|Bitle\d+/);
 };
 
 //========================================================================================