streamRead.c

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/*==================================================================*\
|                EXIP - Embeddable EXI Processor in C                |
|--------------------------------------------------------------------|
|          This work is licensed under BSD 3-Clause License          |
|  The full license terms and conditions are located in LICENSE.txt  |
\===================================================================*/

#include "streamRead.h"
#include "ioUtil.h"

const unsigned char BIT_MASK[] = {  (char) 0x00,    // 0b00000000
                                    (char) 0x01,    // 0b00000001
                                    (char) 0x03,    // 0b00000011
                                    (char) 0x07,    // 0b00000111
                                    (char) 0x0F,    // 0b00001111
                                    (char) 0x1F,    // 0b00011111
                                    (char) 0x3F,    // 0b00111111
                                    (char) 0x7F,    // 0b01111111
                                    (char) 0xFF };  // 0b11111111

errorCode readNextBit(EXIStream* strm, boolean* bit_val)
{
    if(strm->buffer.bufContent <= strm->context.bufferIndx) // the whole buffer is parsed! read another portion
    {
        strm->context.bitPointer = 0;
        strm->context.bufferIndx = 0;
        strm->buffer.bufContent = 0;
        if(strm->buffer.ioStrm.readWriteToStream == NULL)
            return EXIP_BUFFER_END_REACHED;
        strm->buffer.bufContent = strm->buffer.ioStrm.readWriteToStream(strm->buffer.buf, strm->buffer.bufLen, strm->buffer.ioStrm.stream);
        if(strm->buffer.bufContent == 0)
            return EXIP_BUFFER_END_REACHED;
    }

    *bit_val = (strm->buffer.buf[strm->context.bufferIndx] & (1<<REVERSE_BIT_POSITION(strm->context.bitPointer))) != 0;

    moveBitPointer(strm, 1);
    DEBUG_MSG(INFO, DEBUG_STREAM_IO, ("  @%u:%u", (unsigned int) strm->context.bufferIndx, strm->context.bitPointer));
    return EXIP_OK;
}

errorCode readBits(EXIStream* strm, unsigned char n, unsigned int* bits_val)
{
    unsigned int numBytesToBeRead = 1 + ((n + strm->context.bitPointer - 1) / 8);
    unsigned int byteIndx = 1;
    unsigned char *buf;

    if(strm->buffer.bufContent < strm->context.bufferIndx + numBytesToBeRead)
    {
        // The buffer end is reached: there are fewer than n bits left unparsed
        errorCode tmp_err_code = EXIP_UNEXPECTED_ERROR;

        TRY(readEXIChunkForParsing(strm, numBytesToBeRead));
    }

    buf = (unsigned char *) strm->buffer.buf + strm->context.bufferIndx;

    *bits_val = (buf[0] & BIT_MASK[8 - strm->context.bitPointer])<<((numBytesToBeRead-1)*8);

    while(byteIndx < numBytesToBeRead)
    {
        *bits_val += (unsigned int) (buf[byteIndx])<<((numBytesToBeRead-byteIndx-1)*8);
        byteIndx++;
    }

    *bits_val = *bits_val >> (numBytesToBeRead*8 - n - strm->context.bitPointer);

    DEBUG_MSG(INFO, DEBUG_STREAM_IO, (">> %d [0x%X] (%u bits)", *bits_val, *bits_val, n));

    n += strm->context.bitPointer;
    strm->context.bufferIndx += n / 8;
    strm->context.bitPointer = n % 8;

    DEBUG_MSG(INFO, DEBUG_STREAM_IO, ("  @%u:%u\n", (unsigned int) strm->context.bufferIndx, strm->context.bitPointer));

    return EXIP_OK;
}