dd: incorrect seek on oseek=1Bx2x4

[jfinkels]

Coreutils dd v9.4.113-c01ee:

$ echo abcdefghijklm | ../gnu/src/dd oseek=1Bx2x4 bs=5 > out 2> /dev/null && cat out
^@^@^@^@^@^@^@^@abcdefghijklm

(The ^@ are null bytes.)

On uutils dd:

$ echo abcdefghijklm | ./target/debug/dd oseek=1Bx2x4 bs=5 > out 2> /dev/null && cat out
^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@abcdefghijklm

This is from the GNU test suite file tests/dd/bytes.sh.

[matrixhead]

seems like coreutil's dd treats the oseek operand as bytes if it contains a 'B' anywhere in the argument, even though it's says in the man page that it will only do so if the argument ends in a 'B' but in our implementation we only check for the 'B' at the end of the string. In this case 1Bx2x4 'B' appears not at the end of the string so it treats it as blocks and failing the test case