trunc (to float): Wasm text instruction - Content

The trunc instructions, short for truncate, are used for getting the value of a number without its fractional part.

trunc differs from floor when used on negative numbers, floor will round down in those cases while trunc will round up.

There's another trunc instruction that truncates the fractional part of a floating point and converts it to an integer.

{{InteractiveExample("Wat Demo: trunc_float_to_float", "tabbed-taller")}}

wat

(module
  (import "console" "log" (func $log (param f32)))
  (func $main

    f32.const -2.7 ;; load a number onto the stack
    f32.trunc ;; discard everything after the decimal point
    call $log ;; log the result

  )
  (start $main)
)

const url = "{%wasm-url%}";
await WebAssembly.instantiateStreaming(fetch(url), { console });

Syntax

wat

;; load a number onto the stack
f32.const 2.7

;; discard the fractional part (.7)
f32.trunc

;; the top item on the stack will now be 2

Instruction	Binary opcode
`f32.trunc`	`0x8f`
`f64.trunc`	`0x9d`