ZBasicSysLib - page 99 of 361

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ZBasic System Library

ZBasic Microcontrollers

Function returning UnsignedLong

CRC32(data, count, crcPoly, crcInit, crcFlags)

The data bytes to add to the CRC value.

The number of bytes to process.

The CRC polynomial to use.

The initial value of the CRC.

Flag bits that control the CRC computation.

This function computes the CRC value over a number of data bytes using a specified polynomial and

initial value. The values to use for the polynomial and the initial value depend on the style of CRC that

you need to generate. The flags parameter contains bits that control aspects of the CRC computation

as described in the table below.

Flag Values for the CRC Compuation

The input data bytes will be “reflected”.

The final CRC will be “reflected”.

The remaining bits are reserved for future use and should always be zero.

Although this function will typically be used to compute the CRC value for an entire block of data at once,

it may also be used in a byte-by-byte or data burst mode. To do so, you would pass the computed CRC

value from the previous iteration as the initial value. Note, however, that you shouldn’t use the zxRefOut

flag bit in this case. Rather, if you need reflected output you would perform the bit reversal on the final

CRC value when you reach the end of the data stream.

See the discussion of the CRC16() function for additional information.

Dim data(1 to 20) as Byte

Dim crc as UnsignedLong

crc = Not CRC32(data, 10, &H04c11db7, &Hffffffff, zxCRCRefIn Or zxCRCRefOut)

This function is not available in BasicX compatibility mode. Also, on ZX models that are based on the

ATmega32 processor (e.g. the ZX-24) this function is implemented in “user code” (as opposed to being

part of the VM) and is consequently slower than on other ZX models and ZBasic devices generally.