fill: Wasm text instruction

The fill memory instruction sets all bytes in a memory region to a given byte.

The instruction returns no value. It traps (exception) if the indicated memory region is out of bounds.

Syntax

Fill within default memory

wasm
;; Fill region at offset/range in default memory with 255
i32.const 200 ;; The pointer to the region to update
i32.const 255 ;; The value to set each byte to (must be < 256)
i32.const 100 ;; The number of bytes to update
memory.fill ;; Fill default memory

;; Fill default memory using an S-function
(memory.fill (i32.const 200) (i32.const 255) (i32.const 100))

Fill specified memory (if multi-memory supported)

wasm
;; Fill specific memory referenced by its index
i32.const 200 ;; The pointer to the region to update
i32.const 255 ;; The value to set each byte to (must be < 256)
i32.const 100 ;; The number of bytes to update
memory.fill (memory 1) ;; Fill memory with index 1

;; Fill memory referenced by its name
i32.const 200 ;; The pointer to the region to update
i32.const 255 ;; The value to set each byte to (must be < 256)
i32.const 100 ;; The number of bytes to update
memory.fill (memory $memoryName) ;; Fill memory with name "$memoryName"

;; Fill same memory using an S function
(memory.fill (memory $memoryName) (i32.const 200) (i32.const 255) (i32.const 100))

Instructions and opcodes

Instruction Binary opcode
memory.fill 0xFC 0x0b

Specifications

Specification
Unknown specification
# syntax-instr-memory

Browser compatibility

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Note: Memory support in Wasm modules matches the WebAssembly.Memory JavaScript API. The multiMemory key indicates versions in which store can be used with a specified memory.