trunc_f64_s: Wasm numeric instruction

The trunc_f64_s numeric instruction removes the fractional part of an f64 value and outputs it as a signed integer.

This is a separate instruction, trunc, which removes the fractional part of a float and outputs a float.

There are also other truncate integer conversion instructions:

Try it

(module
  (import "console" "log" (func $log (param i32)))
  (func $main

    f64.const 2300044.4 ;; load a number onto the stack
    i32.trunc_f64_s ;; discard decimal part and return signed integer
    call $log ;; log the result

  )
  (start $main)
)

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

Syntax

value_type.trunc_f64_s

value_type

The type of value the instruction is being run on. The following types support trunc_f64_s:

i32
i64

trunc_f64_s

The trunc_f64_s instruction. Must always be included after the value_type and a period (.).

Type

[input] -> [output]

input: The input floating point number.
output: The output integer.

Binary encoding

Instruction	Binary format	Example text => binary
`i32.trunc_f64_s`	`0xaa`	`i32.trunc_f64_s` => `0xaa`
`i64.trunc_f64_s`	`0xb0`	`i64.trunc_f64_s` => `0xb0`

Specifications

WebAssembly Core Specification