截斷(浮點數到整數)

trunc 指令用於將浮點數轉換為整數。它之所以命名為截斷,是因為在轉換過程中會截斷數字的小數部分。此指令有有符號和無符號版本。

還有另一個 trunc 指令,它會在不轉換為整數的情況下截斷浮點數的小數部分。

試一試

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

    f32.const 10.5 ;; push an f32 onto the stack

    i32.trunc_f32_s ;; convert from f32 to signed i32 rounding towards zero (.5 will be lost)

    call $log ;; log the result

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

語法

wat
;; push an f32 onto the stack
f32.const 10.5

;; convert from f32 to signed i32 rounding towards zero (.5 will be lost)
i32.trunc_f32_s

;; the top item on the stack will now be the value 10 of type f32
指令 二進位制操作碼
i32.trunc_f32_s 0xa8
i32.trunc_f32_u 0xa9
i32.trunc_f64_s 0xaa
i32.trunc_f64_u 0xab
i64.trunc_f32_s 0xae
i64.trunc_f32_u 0xaf
i64.trunc_f64_s 0xb0
i64.trunc_f64_u 0xb1