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← Back to Instruction Set: Quick Reference

CAST

Type cast memory value

Opcodes 0x1C-0x1D (2 wire formats)

M[dstOffset] = M[srcOffset] as tag

Details

Changes the type tag of a value. The value itself is preserved if casting to a larger type. When casting to a smaller type, the value is truncated by keeping only the least significant bits that fit in the destination type (equivalent to modulo 2^k where k is the bit-width of the destination type).

Gas Costs

Component Value Scales with
L2 Base 27 -
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
srcOffset Memory offset Memory offset of the value to cast
dstOffset Memory offset Memory offset for casted value
dstTag Type tag Type tag to cast the value to

Wire Formats

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

CAST_8 (Opcode 0x1C):

---
title: "CAST_8"
config:
  packet:
    bitsPerRow: 40
---
packet-beta
0-7: "Opcode (0x1C)"
8-15: "Addressing modes"
16-23: "Operand: srcOffset"
24-31: "Operand: dstOffset"
32-39: "Operand: dstTag"
Loading

CAST_16 (Opcode 0x1D):

---
title: "CAST_16"
config:
  packet:
    bitsPerRow: 56
---
packet-beta
0-7: "Opcode (0x1D)"
8-15: "Addressing modes"
16-31: "Operand: srcOffset"
32-47: "Operand: dstOffset"
48-55: "Operand: dstTag"
Loading

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 (srcOffset, dstOffset) are encoded as follows:

---
title: "Addressing Mode Bitmask"
config:
  packet:
    bitWidth: 128
    bitsPerRow: 8
---
packet-beta
  0: "srcOffset is indirect"
  1: "srcOffset is relative"
  2: "dstOffset is indirect"
  3: "dstOffset is relative"
  4: "Unused"
  5: "Unused"
  6: "Unused"
  7: "Unused"
Loading

Tag Updates

  • T[dstOffset] = dstTag

Error Conditions

  • INVALID_TAG: Destination tag is not a valid TypeTag
  • MEMORY_ACCESS_OUT_OF_RANGE: Memory offset operand exceeds addressable memory

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