From e8ebaeb4974bae9584e4e93af9fc45e06d72cb99 Mon Sep 17 00:00:00 2001
From: Stephen Birarda <commit@birarda.com>
Date: Fri, 15 Mar 2013 12:27:22 -0700
Subject: [PATCH] add OctalCode shared library for octal code operations

---
 shared/src/OctalCode.cpp | 88 ++++++++++++++++++++++++++++++++++++++++
 shared/src/OctalCode.h   | 17 ++++++++
 2 files changed, 105 insertions(+)
 create mode 100644 shared/src/OctalCode.cpp
 create mode 100644 shared/src/OctalCode.h

diff --git a/shared/src/OctalCode.cpp b/shared/src/OctalCode.cpp
new file mode 100644
index 0000000000..7a604bdc09
--- /dev/null
+++ b/shared/src/OctalCode.cpp
@@ -0,0 +1,88 @@
+//
+//  OctalCode.cpp
+//  hifi
+//
+//  Created by Stephen Birarda on 3/15/13.
+//
+//
+
+#include <cmath>
+#include "SharedUtil.h"
+#include "OctalCode.h"
+
+int numberOfThreeBitSectionsInCode(unsigned char * octalCode) {
+    if (*octalCode == 255) {
+        return *octalCode + numberOfThreeBitSectionsInCode(octalCode + 1);
+    } else {
+        return *octalCode;
+    }
+}
+
+int bytesRequiredForCodeLength(unsigned char threeBitCodes) {
+    if (threeBitCodes == 0) {
+        return 1;
+    } else {
+        return 1 + (int)ceilf((threeBitCodes * 3) / 8.0);
+    }
+    
+}
+
+void printOctalCode(unsigned char * octalCode) {
+    for (int i = 1; i < bytesRequiredForCodeLength(*octalCode); i++) {
+        outputBits(octalCode[i]);
+    }
+}
+
+unsigned char * childOctalCode(unsigned char * parentOctalCode, char childNumber) {
+    
+    // find the length (in number of three bit code sequences)
+    // in the parent
+    int parentCodeSections = parentOctalCode != NULL
+        ? numberOfThreeBitSectionsInCode(parentOctalCode)
+        : 0;
+    
+    // get the number of bytes used by the parent octal code
+    int parentCodeBytes = bytesRequiredForCodeLength(parentCodeSections);
+    
+    // child code will have one more section than the parent
+    int childCodeBytes = bytesRequiredForCodeLength(parentCodeSections + 1);
+    
+    // create a new buffer to hold the new octal code
+    unsigned char *newCode = new unsigned char[childCodeBytes];
+    
+    // copy the parent code to the child
+    if (parentOctalCode != NULL) {
+        memcpy(newCode, parentOctalCode, parentCodeBytes);
+    }    
+    
+    // the child octal code has one more set of three bits
+    *newCode = parentCodeSections + 1;
+    
+    if (childCodeBytes > parentCodeBytes) {
+        // we have a new byte due to the addition of the child code
+        // so set it to zero for correct results when shifting later
+        newCode[childCodeBytes - 1] = 0;
+    }
+    
+    // add the child code bits to newCode
+    
+    // find the start bit index
+    int startBit = parentCodeSections * 3;
+    
+    // calculate the amount of left shift required
+    // this will be -1 or -2 if there's wrap
+    char leftShift = 8 - (startBit % 8) - 3;
+    
+    if (leftShift < 0) {
+        // we have a wrap-around to accomodate
+        // right shift for the end of first byte
+        // left shift for beginning of the second
+        newCode[(startBit / 8) + 1] += childNumber >> (-1 * leftShift);
+        newCode[(startBit / 8) + 2] += childNumber << (8 + leftShift);
+    } else {
+        // no wraparound, left shift and add
+        newCode[(startBit / 8) + 1] += (childNumber << leftShift);
+    }
+    
+    return newCode;
+}
diff --git a/shared/src/OctalCode.h b/shared/src/OctalCode.h
new file mode 100644
index 0000000000..910e11b077
--- /dev/null
+++ b/shared/src/OctalCode.h
@@ -0,0 +1,17 @@
+//
+//  OctalCode.h
+//  hifi
+//
+//  Created by Stephen Birarda on 3/15/13.
+//
+//
+
+#ifndef __hifi__OctalCode__
+#define __hifi__OctalCode__
+
+#include <iostream>
+
+void printOctalCode(unsigned char * octalCode);
+unsigned char * childOctalCode(unsigned char * parentOctalCode, char childNumber);
+
+#endif /* defined(__hifi__OctalCode__) */