Clarification: prepending instead of appending, using -O option with negative values? #11
Description
I'm trying to calculate a 4 byte value to PREPEND to a 8192 byte data file so as to get a specified CRC32 value 0x224E16C3 . My reading of the manual made me think I needed to use the option -O -8192 or maybe even -O -8196. But that does not work. Can you please clarify how to get a value to prepend? Test case below.
## create test file with hex AB repeated the entire file perl -e '$x="AB" x 8192; print pack("H*", $x);' > fileAB.8192 hexdump fileAB.8192 ## test regular append-mode crchack fileAB.8192 224E16C3 > test-append crchack test-append # observe that the padding value is appended hexdump test-append ##trying to create a value to PREPEND crchack -O -8192 fileAB.8192 224E16C3 > test-prepend crchack test-prepend # observe that the padding value is appended but I thought it would prepended? hexdump test-prepend crchack -O -8196 fileAB.8192 224E16C3 > test-prepend leads to error message: bits[0]=65568 exceeds message length (65567 bits)