SUB

1// PTO-INSTRUCTION: {"assembly":["sub SrcL, SrcR<{.sw,.uw,.neg}><<<shamt>, ->{t, u, Rd}"],"block":[],"catalog_indices":[436],"catalog_records":[{"asm":"sub SrcL, SrcR<{.sw,.uw,.neg}><<<shamt>, ->{t, u, Rd}","constraints":[],"encoding":[{"index":0,"mask":"0x0000707f","match":"0x00001005","width_bits":32}],"encoding_kind":"L32","fields":[{"name":"RegDst","pieces":[{"instruction_lsb":7,"value_lsb":0,"width":5}],"signedness":"encoding-defined","width":5},{"name":"SrcL","pieces":[{"instruction_lsb":15,"value_lsb":0,"width":5}],"signedness":"encoding-defined","width":5},{"name":"SrcR","pieces":[{"instruction_lsb":20,"value_lsb":0,"width":5}],"signedness":"encoding-defined","width":5},{"name":"SrcRType","pieces":[{"instruction_lsb":25,"value_lsb":0,"width":2}],"signedness":"encoding-defined","width":2},{"name":"shamt","pieces":[{"instruction_lsb":27,"value_lsb":0,"width":5}],"signedness":"encoding-defined","width":5}],"form_id":"sub_32_af383d4a2b42","length_bits":32,"mnemonic":"SUB","semantic_family":"ALU","semantic_group":"ALU","semantic_handler":"ScalarBinary","semantic_summary":"SUB applies the selected right-source transformation before its encoded logical left shift, performs fixed-width subtraction, and publishes the PTO_XLEN result.","status":"accepted"}],"classification":["alu"],"contract":{"block_composition":["none"],"canonical_assembly":["sub SrcL, SrcR<{.sw,.uw,.neg}><<<shamt>, ->{t, u, Rd}"],"defaults":["SrcL, SrcR, SrcRType, shamt, and RegDst are required encoded fields; no field can be omitted.","SrcRType=00 selects .sw, SrcRType=01 selects .uw, SrcRType=10 selects .neg, and SrcRType=11 selects no modifier. An omitted assembly suffix encodes SrcRType=11.","Encoded shamt zero performs no shift; every value from 0 through 31 is assigned."],"encoding_class":"standalone-encoded","examples":["sub a0, a1, ->a2","sub t#1, u#1.neg<<1, ->u","sub zero, a0.sw, ->zero"],"exceptions":["SUB raises no arithmetic exception; transformation, shifting, and the final operation use PTO_XLEN bits modulo 2^PTO_XLEN.","A fixed-bit mismatch or unavailable selected T/U source raises Fault_IllegalInstruction before the destination effect and before TPC advances."],"field_contracts":{},"field_zero_meanings":{"RegDst":"Encoded zero discards the result.","SrcL":"Encoded zero reads the architectural zero GPR.","SrcR":"Encoded zero reads the architectural zero GPR.","SrcRType":"Encoded zero selects .sw and sign-extends SrcR[31:0].","shamt":"Encoded zero performs no shift."},"legality":["SrcL and SrcR codes 0..23 select absolute GPRs, 24..27 select T#1..T#4, and 28..31 select U#1..U#4 without consumption.","RegDst codes 0 and 24..29 discard, code 30 pushes U, code 31 pushes T, and codes 1..23 write GPRs.","All four SrcRType encodings are assigned. The logical family uses .not while the arithmetic family uses .neg; SUB uses .neg.","Every five-bit shamt value from 0 through 31 is legal."],"memory_effects":["none"],"operands":[{"field":"RegDst","role":"Reg5 destination or discard"},{"field":"SrcL","role":"left Reg5 source"},{"field":"SrcR","role":"right Reg5 source"},{"field":"SrcRType","role":"right-source transformation selector"},{"field":"shamt","role":"post-transformation logical-left-shift amount"}],"ordering":["Snapshot both sources before the destination effect so duplicate sources, destination aliases, and queue publication use pre-instruction values.","Publish the result, then advance TPC by four bytes."],"standalone_opcode":true,"state_effects":["Transform SrcR, perform the logical left shift, and subtract the shifted value from SrcL modulo 2^PTO_XLEN.","Apply the selected SrcRType transformation before the logical left shift. The transformation and shift affect SrcR only; SrcL is unchanged before the final operation.","Destination codes 0 and 24..29 discard, code 30 pushes U, code 31 pushes T, and codes 1..23 write GPRs; source queues are non-consuming.","No memory, reservation, descriptor, numeric-flag, trap, block, privilege, or control-flow state changes except the successful TPC advance."]},"depends_on":["PTO-BLOCK-MODEL-SCHEMA-PROFILE-ENCODING"],"id":"PTO-SCALAR-SUB","mnemonic":"SUB","summary":"SUB applies the selected right-source transformation before its encoded logical left shift, performs fixed-width subtraction, and publishes the PTO_XLEN result.","surface":"scalar"}2// PTO-REVIEW: {"review_method":"formal-definition-read","outcome":"FORMAL-COMPLETE","reviewed_fields":["assembly","encoding","defaults","operation","state","memory","ordering","faults","reserved"]}3// NDF-BEGIN: PTO-SUB-ADR-CONTRACT-0014// ndf: kind=contract level=L1 layer=scalar status=accepted5// Decisions: ADR-0026.6// SUB MUST snapshot its scalar sources, apply its mnemonic-owned7// width, immediate, modifier, and wrapping rule, then publish through the8// assigned destination or commit effect in alias-safe order.9// NDF-END: PTO-SUB-ADR-CONTRACT-00110// DOC-BEGIN: decode11readonly func InstructionContractOperation_SUB()12    => ScalarOperation13begin14    return ScalarOperation_SUB;15end;16// DOC-END: decode17// DOC-BEGIN: operation18readonly func InstructionContractHandler_SUB()19    => ScalarSemanticHandler20begin21    return ScalarHandler_ScalarBinary;22end;23
24pure func InstructionContractRightModifier_SUB(encoded: bits(2))25    => ScalarRightModifier26begin27    case encoded of28        when '00' => return ScalarRight_SignedWord;29        when '01' => return ScalarRight_UnsignedWord;30        when '10' => return ScalarRight_NegateOrNot;31        when '11' => return ScalarRight_None;32    end;33end;34
35pure func InstructionContractPreparedRight_SUB(36    right: Word,37    encoded_modifier: bits(2),38    shift_amount: integer {0..31})39    => Word40begin41    let modifier = InstructionContractRightModifier_SUB(encoded_modifier);42    let transformed = ApplyScalarRightModifier(right, modifier, FALSE);43    let shifted = LSL(transformed, shift_amount);44    return shifted;45end;46
47pure func InstructionContractResult_SUB(48    left: Word,49    right: Word,50    encoded_modifier: bits(2),51    shift_amount: integer {0..31})52    => Word53begin54    let prepared_right = InstructionContractPreparedRight_SUB(55        right,56        encoded_modifier,57        shift_amount);58    return ScalarBinary(ScalarBinary_SUB, left, prepared_right);59end;60
61pure func InstructionContractIsLogicalFamily_SUB()62    => boolean63begin64    return FALSE;65end;66
67pure func InstructionContractIsWordOperation_SUB()68    => boolean69begin70    return FALSE;71end;72// DOC-END: operation73