Function checkEncoding

deps/v8/test/mjsunit/wasm/stringrefs-exec.js:792–830

(str, slice, start, length)

  }

  function checkEncoding(str, slice, start, length) {
    let bytes = encodeWtf16LE(slice);
    function clearMemory(low, high) {
      for (let i = low; i < high; i++) {
        memory[i] = 0;
      }
    }
    function assertMemoryBytesZero(low, high) {
      for (let i = low; i < high; i++) {
        assertEquals(0, memory[i]);
      }
    }
    function checkMemory(offset, bytes) {
      let slop = 64;
      assertMemoryBytesZero(Math.max(0, offset - slop), offset);
      for (let i = 0; i < bytes.length; i++) {
        assertEquals(bytes[i], memory[offset + i]);
      }
      assertMemoryBytesZero(offset + bytes.length,
                            Math.min(memory.length,
                                     offset + bytes.length + slop));
    }

    for (let offset of [0, 42, memory.length - bytes.length]) {
      assertEquals(slice.length,
                   instance.exports.encode(str, offset, start, length));
      checkMemory(offset, bytes);
      clearMemory(offset, offset + bytes.length);
    }

    assertThrows(() => instance.exports.encode(str, 1, start, length),
                 WebAssembly.RuntimeError,
                 "operation does not support unaligned accesses");
    assertThrows(
        () => instance.exports.encode(str, memory.length - bytes.length + 2,
                                      start, length),
        WebAssembly.RuntimeError, "memory access out of bounds");
    checkMemory(memory.length - bytes.length - 2, []);
  }
  checkEncoding("fox", "f", 0, 1);
  checkEncoding("fox", "fo", 0, 2);
  checkEncoding("fox", "fox", 0, 3);