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Annotation of XNU/iokit/Families/IOHIDSystem/IOHIDDescriptorParser/HIDGetData.c, revision 1.1

1.1     ! root        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 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:                (BWS)   Brent Schorsch
        !            42: 
        !            43:        Change History (most recent first):
        !            44: 
        !            45:          <USB2>          3/5/99        BWS             [2311353]  HIDGetData not masking properly, so not work at all
        !            46:          <USB1>          3/5/99        BWS             first checked in
        !            47: */
        !            48: 
        !            49: #include "HIDLib.h"
        !            50: 
        !            51: /*
        !            52:  *------------------------------------------------------------------------------
        !            53:  *
        !            54:  * HIDGetData - Get a single data item from a report
        !            55:  *
        !            56:  *      Input:
        !            57:  *                       psReport                              - The report
        !            58:  *                       iReportLength                 - The length of the report
        !            59:  *                       iStart                                - Start Bit in report
        !            60:  *                       iSize                                 - Number of Bits
        !            61:  *                       piValue                               - The place to write the data
        !            62:  *                       bSignExtend                   - Sign extend?
        !            63:  *      Output:
        !            64:  *                       piValue                               - The data
        !            65:  *      Returns:
        !            66:  *                       kHidP_Success                 - Success
        !            67:  *                       kHidP_NullPointer             - Argument, Pointer was Null
        !            68:  *
        !            69:  *------------------------------------------------------------------------------
        !            70: */
        !            71: OSStatus HIDGetData(void * report, UInt32 iReportLength,
        !            72:                                                 UInt32 iStart, UInt32 iSize, SInt32 *piValue,
        !            73:                                                 Boolean bSignExtend)
        !            74: {
        !            75:        Byte * psReport = report;
        !            76:        unsigned data;
        !            77:        unsigned iSignBit;
        !            78:        unsigned iExtendMask;
        !            79:     unsigned iStartByte = iStart/8;
        !            80:     unsigned startBit = iStart&7;
        !            81:     unsigned iLastBit = iStart + iSize - 1;
        !            82:     unsigned iLastByte = iLastBit/8;
        !            83:     int iCurrentByte;          // needs to be signed, we terminate loop on -1
        !            84:     unsigned iMask;
        !            85: 
        !            86:        // Check the parameters
        !            87:        if ((iSize == 0) || (iLastByte >= iReportLength) || (iLastByte < iStartByte))
        !            88:                return kHIDBadParameterErr;
        !            89: 
        !            90:        // Pick up the data bytes backwards
        !            91:     data = 0;
        !            92:     for (iCurrentByte = iLastByte; iCurrentByte >= (int) iStartByte; iCurrentByte--)
        !            93:     {
        !            94:         data <<= 8;
        !            95: 
        !            96:                iMask = 0xff;   //  1111 1111 initial mask
        !            97:                // if this is the 'last byte', then we need to mask off the top part of the byte
        !            98:                // to find the mask, we: find the position in this byte (lastBit % 8)
        !            99:                // then shift one to the left that many times plus one (to get one bit further)
        !           100:                // then subtract 1 to get all ones starting from the lastBit to the least signif bit
        !           101:                // ex: if iLastBit is 9, or iLastBit is 15, then we get: 
        !           102:                //                                      1                                       7                       (x % 8)
        !           103:                //                           0000 0100                  1 0000 0000             (1 << (x + 1))
        !           104:                //                               0000 0011                      0 1111 1111             (x - 1)
        !           105:                if (iCurrentByte == iLastByte)
        !           106:                        iMask = ((1 << (((unsigned) iLastBit % 8) + 1)) - 1);
        !           107: 
        !           108:         data |= (unsigned) psReport[iCurrentByte] & iMask;
        !           109:        }
        !           110: 
        !           111:        // Shift to the right to byte align the least significant bit
        !           112:        data >>= startBit;
        !           113: 
        !           114:        // Sign extend the report item
        !           115:        if (bSignExtend)
        !           116:        {
        !           117:                iSignBit = 1;
        !           118:                if (iSize > 1)
        !           119:                        iSignBit <<= (iSize-1);
        !           120:                iExtendMask = (iSignBit << 1) - 1;
        !           121:                if ((data & iSignBit)==0)
        !           122:                        data &= iExtendMask;
        !           123:                else
        !           124:                        data |= ~iExtendMask;
        !           125:        }
        !           126: 
        !           127:        // Return the value
        !           128:        *piValue = (SInt32) data;
        !           129: 
        !           130:        return kHIDSuccess;
        !           131: }

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