The bits of the source (second operand/SRC1 when short form, first operand/SRC2 when long form) are rotated left by a number indicated by the 5 MSB of either the first operand/SRC1 (short form) or the Imm16 value (long form).
The result is written either to SRC2 (short form) or to SRC1 (long form).
The ROR instruction rotates the bits right.