"""
RISC-V Encoding recipes.

The encoding recipes defined here more or less correspond to the RISC-V native
instruction formats described in the reference:

    The RISC-V Instruction Set Manual
    Volume I: User-Level ISA
    Version 2.1
"""
from __future__ import absolute_import
from cdsl.isa import EncRecipe
from cdsl.predicates import IsSignedInt
from base.formats import Binary, BinaryImm, ReturnReg
from .registers import GPR

# The low 7 bits of a RISC-V instruction is the base opcode. All 32-bit
# instructions have 11 as the two low bits, with bits 6:2 determining the base
# opcode.
#
# Encbits for the 32-bit recipes are opcode[6:2] | (funct3 << 5) | ...
# The functions below encode the encbits.


def LOAD(funct3):
    # type: (int) -> int
    assert funct3 <= 0b111
    return 0b00000 | (funct3 << 5)


def STORE(funct3):
    # type: (int) -> int
    assert funct3 <= 0b111
    return 0b01000 | (funct3 << 5)


def BRANCH(funct3):
    # type: (int) -> int
    assert funct3 <= 0b111
    return 0b11000 | (funct3 << 5)


def JALR(funct3=0):
    # type: (int) -> int
    assert funct3 <= 0b111
    return 0b11001 | (funct3 << 5)


def OPIMM(funct3, funct7=0):
    # type: (int, int) -> int
    assert funct3 <= 0b111
    return 0b00100 | (funct3 << 5) | (funct7 << 8)


def OPIMM32(funct3, funct7=0):
    # type: (int, int) -> int
    assert funct3 <= 0b111
    return 0b00110 | (funct3 << 5) | (funct7 << 8)


def OP(funct3, funct7):
    # type: (int, int) -> int
    assert funct3 <= 0b111
    assert funct7 <= 0b1111111
    return 0b01100 | (funct3 << 5) | (funct7 << 8)


def OP32(funct3, funct7):
    # type: (int, int) -> int
    assert funct3 <= 0b111
    assert funct7 <= 0b1111111
    return 0b01110 | (funct3 << 5) | (funct7 << 8)


# R-type 32-bit instructions: These are mostly binary arithmetic instructions.
# The encbits are `opcode[6:2] | (funct3 << 5) | (funct7 << 8)
R = EncRecipe('R', Binary, ins=(GPR, GPR), outs=GPR)

# R-type with an immediate shift amount instead of rs2.
Rshamt = EncRecipe('Rshamt', BinaryImm, ins=GPR, outs=GPR)

I = EncRecipe(
        'I', BinaryImm, ins=GPR, outs=GPR,
        instp=IsSignedInt(BinaryImm.imm, 12))

# I-type encoding for `jalr` as a return instruction. We won't use the
# immediate offset.
# The variable return values are not encoded.
Iret = EncRecipe('Iret', ReturnReg, ins=GPR, outs=())