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← Back to Instruction Set: Quick Reference

NOTEHASHEXISTS

Check existence of note hash

Opcode 0x31

M[existsOffset] = noteHashTree.exists(M[noteHashOffset], M[leafIndexOffset]) ? 1 : 0

Details

Performs a read of the Note Hash Tree to query whether the specified note hash exists at the given leaf index. Since this opcode checks for existence at a specified leafIndex, it is not limited to checking for note hashes of only the currently executing contract. Note that it is difficult to check for existence of a note hash emitted earlier in the same block because this opcode requires leafIndex. If the leaf index exceeds the maximum tree size, the result is 0 (does not exist). Note hash must be FIELD, leaf index must be Uint64. Result is Uint1.

Gas Costs

Component Value Scales with
L2 Base 504 -
DA Base 0 -
L2 Addressing 3 3 L2 gas per indirect memory offset
3 L2 gas per relative memory offset

* See Gas Metering for details on how gas costs are computed and applied.

Operands

Name Type Description
noteHashOffset Memory offset Memory offset of the note hash to check
leafIndexOffset Memory offset Memory offset of the leaf index in the note hash tree
existsOffset Memory offset Memory offset where the result (0 or 1) will be written

Wire Formats

See Wire Format page for an explanation of wire format variants and opcode naming (e.g., why ADD_8 vs ADD_16).

NOTEHASHEXISTS (Opcode 0x31):

---
title: "NOTEHASHEXISTS"
config:
  packet:
    bitsPerRow: 64
---
packet-beta
0-7: "Opcode (0x31)"
8-15: "Addressing modes"
16-31: "Operand: noteHashOffset"
32-47: "Operand: leafIndexOffset"
48-63: "Operand: existsOffset"
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Addressing Modes

See Addressing page for a detailed explanation.

8-bit bitmask: 2 bits per memory offset operand (indirect flag + relative flag)

Memory offset operands (noteHashOffset, leafIndexOffset, existsOffset) are encoded as follows:

---
title: "Addressing Mode Bitmask"
config:
  packet:
    bitWidth: 128
    bitsPerRow: 8
---
packet-beta
  0: "noteHashOffset is indirect"
  1: "noteHashOffset is relative"
  2: "leafIndexOffset is indirect"
  3: "leafIndexOffset is relative"
  4: "existsOffset is indirect"
  5: "existsOffset is relative"
  6: "Unused"
  7: "Unused"
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Tag Checks

  • T[noteHashOffset] == FIELD
  • T[leafIndexOffset] == UINT64

Tag Updates

  • T[existsOffset] = UINT1

Error Conditions

  • INVALID_TAG: Note hash is not FIELD or leaf index is not Uint64
  • MEMORY_ACCESS_OUT_OF_RANGE: Memory offset operand exceeds addressable memory

← Back to Instruction Set: Quick Reference