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##### 9.37.3.1 Register naming

The `as` recognizes a number of predefined symbols for the various processor registers. A register specification in one of the instruction formats is an unsigned integer between 0 and 15. The specific instruction and the position of the register in the instruction format denotes the type of the register. The register symbols are prefixed with ‘`%`’:

         %rN the 16 general purpose registers, 0 <= N <= 15

    %fN the 16 floating point registers, 0 <= N <= 15

    %aN the 16 access registers, 0 <= N <= 15

    %cN the 16 control registers, 0 <= N <= 15

    %lit an alias for the general purpose register %r13

    %sp an alias for the general purpose register %r15