iokit/Families/IOHIDSystem/IOHIDDescriptorParser/HIDGetData.c

   1 /*
   2  * Copyright (c) 1998-2000 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * The contents of this file constitute Original Code as defined in and
   7  * are subject to the Apple Public Source License Version 1.1 (the
   8  * "License").  You may not use this file except in compliance with the
   9  * License.  Please obtain a copy of the License at
  10  * http://www.apple.com/publicsource and read it before using this file.
  11  *
  12  * This Original Code and all software distributed under the License are
  13  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  14  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  15  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  16  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
  17  * License for the specific language governing rights and limitations
  18  * under the License.
  19  *
  20  * @APPLE_LICENSE_HEADER_END@
  21  */
  22 /*
  23         File:           HIDGetData.c
  24
  25         Contains:       xxx put contents here xxx
  26
  27         Version:        xxx put version here xxx
  28
  29         Copyright:      © 1999-2000 by Apple Computer, Inc., all rights reserved.
  30
  31         File Ownership:
  32
  33                 DRI:                            xxx put dri here xxx
  34
  35                 Other Contact:          xxx put other contact here xxx
  36
  37                 Technology:                     xxx put technology here xxx
  38
  39         Writers:
  40
  41                 (KH)    Keithen Hayenga
  42                 (BWS)   Brent Schorsch
  43
  44         Change History (most recent first):
  45
  46           <USB3>        12/12/00        KH              Correct cast of void *
  47           <USB2>          3/5/99        BWS             [2311353]  HIDGetData not masking properly, so not work at all
  48           <USB1>          3/5/99        BWS             first checked in
  49 */
  50
  51 #include "HIDLib.h"
  52
  53 /*
  54  *------------------------------------------------------------------------------
  55  *
  56  * HIDGetData - Get a single data item from a report
  57  *
  58  *       Input:
  59  *                        psReport                              - The report
  60  *                        iReportLength                 - The length of the report
  61  *                        iStart                                - Start Bit in report
  62  *                        iSize                                 - Number of Bits
  63  *                        piValue                               - The place to write the data
  64  *                        bSignExtend                   - Sign extend?
  65  *       Output:
  66  *                        piValue                               - The data
  67  *       Returns:
  68  *                        kHidP_Success                 - Success
  69  *                        kHidP_NullPointer             - Argument, Pointer was Null
  70  *
  71  *------------------------------------------------------------------------------
  72 */
  73 OSStatus HIDGetData(void * report, UInt32 iReportLength,
  74                                                  UInt32 iStart, UInt32 iSize, SInt32 *piValue,
  75                                                  Boolean bSignExtend)
  76 {
  77         Byte * psReport = (Byte *)report;
  78         unsigned data;
  79         unsigned iSignBit;
  80         unsigned iExtendMask;
  81     unsigned iStartByte = iStart/8;
  82     unsigned startBit = iStart&7;
  83     unsigned iLastBit = iStart + iSize - 1;
  84     unsigned iLastByte = iLastBit/8;
  85     int iCurrentByte;           // needs to be signed, we terminate loop on -1
  86     unsigned iMask;
  87
  88         // Check the parameters
  89         if ((iSize == 0) || (iLastByte >= iReportLength) || (iLastByte < iStartByte))
  90                 return kHIDBadParameterErr;
  91
  92         // Pick up the data bytes backwards
  93     data = 0;
  94     for (iCurrentByte = iLastByte; iCurrentByte >= (int) iStartByte; iCurrentByte--)
  95     {
  96         data <<= 8;
  97
  98                 iMask = 0xff;   //  1111 1111 initial mask
  99                 // if this is the 'last byte', then we need to mask off the top part of the byte
 100                 // to find the mask, we: find the position in this byte (lastBit % 8)
 101                 // then shift one to the left that many times plus one (to get one bit further)
 102                 // then subtract 1 to get all ones starting from the lastBit to the least signif bit
 103                 // ex: if iLastBit is 9, or iLastBit is 15, then we get:
 104                 //                                      1                                       7                       (x % 8)
 105                 //                           0000 0100                  1 0000 0000             (1 << (x + 1))
 106                 //                               0000 0011                      0 1111 1111             (x - 1)
 107                 if (iCurrentByte == iLastByte)
 108                         iMask = ((1 << (((unsigned) iLastBit % 8) + 1)) - 1);
 109
 110         data |= (unsigned) psReport[iCurrentByte] & iMask;
 111         }
 112
 113         // Shift to the right to byte align the least significant bit
 114         data >>= startBit;
 115
 116         // Sign extend the report item
 117         if (bSignExtend)
 118         {
 119                 iSignBit = 1;
 120                 if (iSize > 1)
 121                         iSignBit <<= (iSize-1);
 122                 iExtendMask = (iSignBit << 1) - 1;
 123                 if ((data & iSignBit)==0)
 124                         data &= iExtendMask;
 125                 else
 126                         data |= ~iExtendMask;
 127         }
 128
 129         // Return the value
 130         *piValue = (SInt32) data;
 131
 132         return kHIDSuccess;
 133 }