64-bit RISC-V
This chapter has discussed the 32-bit RV32I architecture and instruction set and several important extensions. The RV64I instruction set expands RV32I to a 64-bit architecture. As in RV32I, instructions are 32 bits wide. In fact, the RV64I instruction set is almost entirely the same as RV32I, except for these significant differences:
- Integer registers are widened to 64 bits.
- Addresses are widened to 64 bits.
- Bit shift counts in instruction opcodes increase in size from 5 to 6 bits.
- Several new instructions are provided to operate on 32-bit values in a manner equivalent to RV32I. These instructions are necessary because most instructions in RV64I operate on 64-bit values and there are many situations in which it is necessary to operate efficiently on 32-bit values. These word-oriented instructions have an opcode mnemonic suffix of
W. TheW-suffix instructions produce signed 32-bit results. These 32-bit values are sign-extended (even if they...
