BCNT

assembly

[
  "bcnt srcL,  M, N, ->{t, u, Rd}"
]

block

[]

catalog_indices

[
  14
]

catalog_records

[
  {
    "asm": "bcnt srcL,  M, N, ->{t, u, Rd}",
    "constraints": [],
    "encoding": [
      {
        "index": 0,
        "mask": "0x0000707f",
        "match": "0x00006067",
        "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": "imml",
        "pieces": [
          {
            "instruction_lsb": 20,
            "value_lsb": 0,
            "width": 6
          }
        ],
        "signedness": "encoding-defined",
        "width": 6
      },
      {
        "name": "imms",
        "pieces": [
          {
            "instruction_lsb": 26,
            "value_lsb": 0,
            "width": 6
          }
        ],
        "signedness": "encoding-defined",
        "width": 6
      }
    ],
    "form_id": "bcnt_32_e0b06e436a5b",
    "length_bits": 32,
    "mnemonic": "BCNT",
    "semantic_family": "ALU",
    "semantic_group": "ALU",
    "semantic_handler": "CountBitfield",
    "semantic_summary": "BCNT counts set bits in an independently selected wrapping scalar field and publishes the XLEN population count.",
    "status": "accepted"
  }
]

classification

[
  "alu"
]

contract

{
  "block_composition": [
    "none"
  ],
  "canonical_assembly": [
    "bcnt srcL,  M, N, ->{t, u, Rd}"
  ],
  "defaults": [
    "SrcL, imml, imms, and RegDst are required encoded fields; no field can be omitted.",
    "imml encodes N minus one, so raw values 0 through 63 select widths 1 through 64; encoded zero selects N=1.",
    "imms directly encodes M from 0 through 63; encoded zero selects source bit zero."
  ],
  "encoding_class": "standalone-encoded",
  "examples": [
    "bcnt a0, 0, 64, ->a1",
    "bcnt t#1, 60, 8, ->u",
    "bcnt zero, 0, 1, ->zero"
  ],
  "exceptions": [
    "An unavailable selected T/U source raises Fault_IllegalInstruction before the destination effect and before TPC advances.",
    "BCNT raises no arithmetic, memory, alignment, permission, or control-flow exception."
  ],
  "field_contracts": {},
  "field_zero_meanings": {
    "RegDst": "Encoded zero discards the result.",
    "SrcL": "Encoded zero reads the architectural zero GPR.",
    "imml": "Encoded zero selects a one-bit field.",
    "imms": "Encoded zero starts the selected field at source bit zero."
  },
  "legality": [
    "SrcL 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, codes 1..23 write GPRs, code 30 pushes U, and code 31 pushes T.",
    "Every imml and imms value is assigned. The selected N-bit field begins at bit M and wraps through bit 63 to bit 0."
  ],
  "memory_effects": [
    "none"
  ],
  "operands": [
    {
      "field": "RegDst",
      "role": "Reg5 destination or discard"
    },
    {
      "field": "SrcL",
      "role": "Reg5 source"
    },
    {
      "field": "imml",
      "role": "selected field width N minus one"
    },
    {
      "field": "imms",
      "role": "selected field starting bit M"
    }
  ],
  "ordering": [
    "Snapshot SrcL before any destination effect so a GPR alias or a T/U destination push observes the pre-instruction source value.",
    "Publish the result, then advance TPC by four bytes."
  ],
  "standalone_opcode": true,
  "state_effects": [
    "Extract the N-bit field beginning at bit M, wrapping from bit 63 to bit 0, then count every set bit in the selected field. An all-zero selected field returns zero and an all-one selected field returns N.",
    "Publish the complete XLEN result through the common Reg5 destination map. Relative sources are non-consuming; only a T or U destination push changes a temporary queue.",
    "No memory, reservation, descriptor, numeric-status, block, privilege, branch-target, or other control state changes. Successful execution advances TPC by four bytes."
  ]
}

depends_on

[
  "PTO-BLOCK-MODEL-SCHEMA-PROFILE-ENCODING"
]

id

PTO-SCALAR-BCNT

mnemonic

BCNT

summary

BCNT counts set bits in an independently selected wrapping scalar field and publishes the XLEN population count.

surface

scalar

{
  "classification": [
    "alu"
  ],
  "documentation": "docs/scalar/alu/BCNT.md",
  "id": "PTO-SCALAR-BCNT",
  "instruction_contract": {
    "artifact": "spec/evidence/instruction-contract-closure.json",
    "mnemonic": "BCNT",
    "ndf_clause": "PTO-INST-SCALAR-BCNT"
  },
  "mnemonic": "BCNT",
  "readiness_subjects": [
    "ADR-0025",
    "ADR-0026",
    "ADR-0059",
    "ADR-0084"
  ],
  "semantic_tests": [
    "PTO-AVS-SCALAR-BCNT-READINESS-001",
    "PTO-AVS-SCALAR-BCNT-SELECTORS-001",
    "PTO-AVS-SCALAR-BCNT-WRAP-001"
  ],
  "source": "asl/scalar/alu/BCNT.asl",
  "surface": "scalar",
  "tests": [
    "PTO-AVS-SCALAR-BCNT-DECODE-001",
    "PTO-AVS-SCALAR-BCNT-READINESS-001",
    "PTO-AVS-SCALAR-BCNT-SELECTORS-001",
    "PTO-AVS-SCALAR-BCNT-WRAP-001"
  ]
}