87 lines
3.3 KiB
Python
87 lines
3.3 KiB
Python
# MIT License
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#
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# Copyright (c) 2023 Neil Webber
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#
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# Permission is hereby granted, free of charge, to any person obtaining a copy
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# of this software and associated documentation files (the "Software"), to deal
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# in the Software without restriction, including without limitation the rights
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# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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# copies of the Software, and to permit persons to whom the Software is
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# furnished to do so, subject to the following conditions:
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#
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# The above copyright notice and this permission notice shall be included in
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# all copies or substantial portions of the Software.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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# SOFTWARE.
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# These tables are helpful to have for assembler, disassembler, etc
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BRANCH_CODES = {
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'br': 0o000400,
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'bne': 0o001000,
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'beq': 0o001400,
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'bpl': 0o100000,
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'bmi': 0o100400,
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'bvc': 0o102000,
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'bvs': 0o102400,
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'bcc': 0o103000,
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'bhis': 0o103000,
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'bcs': 0o103400,
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'blo': 0o103400,
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'bge': 0o002000,
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'blt': 0o002400,
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'bgt': 0o003000,
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'ble': 0o003400,
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'bhi': 0o101000,
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'blos': 0o101400
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}
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# There are some duplicates and they are chosen arbitrarily by this:
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BRANCH_NAMES = {v: k for k, v in BRANCH_CODES.items()}
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# keyed by masked "base code" (upper byte), not shifted
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_brconds = {
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# NOTE: 000400 case is handled in op000 dispatch separately
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# 0o000400: lambda n, z, v, c: True, # BR
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0o001000: lambda n, z, v, c: not z, # BNE
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0o001400: lambda n, z, v, c: z, # BEQ
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0o100000: lambda n, z, v, c: not n, # BPL
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0o100400: lambda n, z, v, c: n, # BMI
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0o102000: lambda n, z, v, c: not v, # BVC
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0o102400: lambda n, z, v, c: v, # BVS
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0o103000: lambda n, z, v, c: not c, # BCC
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0o103400: lambda n, z, v, c: c, # BCS
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# CAUTION: Python XOR ("^") is bitwise; hence bool() != for ^
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0o002000: lambda n, z, v, c: bool(n) == bool(v), # BGE
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0o002400: lambda n, z, v, c: bool(n) != bool(v), # BLT
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0o003000: lambda n, z, v, c: (bool(n) == bool(v)) and not z, # BGT
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0o003400: lambda n, z, v, c: (bool(n) != bool(v)) or z, # BLE
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0o101000: lambda n, z, v, c: not (c or z), # BHI
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0o101400: lambda n, z, v, c: c or z, # BLOS
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# NOTE: These two are the same as BCC/BCS respectively
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# 0o103000: lambda n, z, v, c: not c, # BHIS
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# 0o103400: lambda n, z, v, c: c, # BLO
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}
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def branches(cpu, inst):
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branch(cpu, inst, _brconds[inst & 0o177400])
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def branch(cpu, inst, condition):
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if condition(cpu.psw_n, cpu.psw_z, cpu.psw_v, cpu.psw_c):
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offset = (inst & 0o377) * 2
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if offset >= 256: # i.e., was a negative 8-bit value
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offset -= 512
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cpu.r[7] = cpu.u16add(cpu.r[7], offset)
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