1/*
2 * @APPLE_LICENSE_HEADER_START@
3 *
4 * Copyright (c) 1999-2012 Apple Computer, Inc.  All Rights Reserved.
5 *
6 * This file contains Original Code and/or Modifications of Original Code
7 * as defined in and that are subject to the Apple Public Source License
8 * Version 2.0 (the 'License'). You may not use this file except in
9 * compliance with the License. Please obtain a copy of the License at
10 * http://www.opensource.apple.com/apsl/ and read it before using this
11 * file.
12 *
13 * The Original Code and all software distributed under the License are
14 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
15 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
16 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
18 * Please see the License for the specific language governing rights and
19 * limitations under the License.
20 *
21 * @APPLE_LICENSE_HEADER_END@
22 */
23/*
24	File:		HIDGetData.c
25
26	Contains:	xxx put contents here xxx
27
28	Version:	xxx put version here xxx
29
30	Copyright:	� 1999-2000 by Apple Computer, Inc., all rights reserved.
31
32	File Ownership:
33
34		DRI:				xxx put dri here xxx
35
36		Other Contact:		xxx put other contact here xxx
37
38		Technology:			xxx put technology here xxx
39
40	Writers:
41
42		(KH)	Keithen Hayenga
43		(BWS)	Brent Schorsch
44
45	Change History (most recent first):
46
47	  <USB3>	12/12/00	KH		Correct cast of void *
48	  <USB2>	  3/5/99	BWS		[2311353]  HIDGetData not masking properly, so not work at all
49	  <USB1>	  3/5/99	BWS		first checked in
50*/
51
52#include "HIDLib.h"
53
54/*
55 *------------------------------------------------------------------------------
56 *
57 * HIDGetData - Get a single data item from a report
58 *
59 *	 Input:
60 *			  psReport				- The report
61 *			  iReportLength			- The length of the report
62 *			  iStart				- Start Bit in report
63 *			  iSize					- Number of Bits
64 *			  piValue				- The place to write the data
65 *			  bSignExtend			- Sign extend?
66 *	 Output:
67 *			  piValue				- The data
68 *	 Returns:
69 *			  kHidP_Success			- Success
70 *			  kHidP_NullPointer		- Argument, Pointer was Null
71 *
72 *------------------------------------------------------------------------------
73*/
74OSStatus HIDGetData(void * report, IOByteCount iReportLength,
75						 UInt32 iStart, UInt32 iSize, SInt32 *piValue,
76						 Boolean bSignExtend)
77{
78	UInt8 * psReport = (UInt8 *)report;
79	unsigned data;
80	unsigned iSignBit;
81	unsigned iExtendMask;
82    unsigned iStartByte = iStart/8;
83    unsigned startBit = iStart&7;
84    unsigned iLastBit = iStart + iSize - 1;
85    unsigned iLastByte = iLastBit/8;
86    int iCurrentByte;		// needs to be signed, we terminate loop on -1
87    unsigned iMask;
88
89	// Check the parameters
90	if ((iSize == 0) || (iLastByte >= iReportLength) || (iLastByte < iStartByte))
91		return kHIDBadParameterErr;
92
93	// Pick up the data bytes backwards
94    data = 0;
95    for (iCurrentByte = iLastByte; iCurrentByte >= (int) iStartByte; iCurrentByte--)
96    {
97        data <<= 8;
98
99		iMask = 0xff;	//  1111 1111 initial mask
100		// if this is the 'last byte', then we need to mask off the top part of the byte
101		// to find the mask, we: find the position in this byte (lastBit % 8)
102		// then shift one to the left that many times plus one (to get one bit further)
103		// then subtract 1 to get all ones starting from the lastBit to the least signif bit
104		// ex: if iLastBit is 9, or iLastBit is 15, then we get:
105		// 					1					7			(x % 8)
106		//			     0000 0100			1 0000 0000		(1 << (x + 1))
107		//				 0000 0011			0 1111 1111		(x - 1)
108		if (iCurrentByte == iLastByte)
109			iMask = ((1 << (((unsigned) iLastBit % 8) + 1)) - 1);
110
111        data |= (unsigned) psReport[iCurrentByte] & iMask;
112	}
113
114	// Shift to the right to byte align the least significant bit
115	data >>= startBit;
116
117	// Sign extend the report item
118	if (bSignExtend)
119	{
120		iSignBit = 1;
121		if (iSize > 1)
122			iSignBit <<= (iSize-1);
123		iExtendMask = (iSignBit << 1) - 1;
124		if ((data & iSignBit)==0)
125			data &= iExtendMask;
126		else
127			data |= ~iExtendMask;
128	}
129
130	// Return the value
131	*piValue = (SInt32) data;
132
133	return kHIDSuccess;
134}
135