ndk 17.0.4的比较分析

Question

下面我有一个关于比较的问题。

AK_FORCE_INLINE static int intArrayToCharArray(const int *const source, const int sourceSize,
    char *dest, const int destSize) {
// We want to always terminate with a 0 char, so stop one short of the length to make
// sure there is room.
const int destLimit = destSize - 1;
int si = 0;
int di = 0;
while (si < sourceSize && di < destLimit && 0 != source[si]) {
    const int codePoint = source[si++];
    if (codePoint < 0x7F) { // One byte
        dest[di++] = codePoint;
    } else if (codePoint < 0x7FF) { // Two bytes
        if (di + 1 >= destLimit) break;
        dest[di++] = 0xC0 + (codePoint >> 6);
        dest[di++] = 0x80 + (codePoint & 0x3F);
    } else if (codePoint < 0xFFFF) { // Three bytes
        if (di + 2 >= destLimit) break;
        dest[di++] = 0xE0 + (codePoint >> 12);
        dest[di++] = 0x80 + ((codePoint >> 6) & 0x3F);
        dest[di++] = 0x80 + (codePoint & 0x3F);
    } else if (codePoint <= 0x1FFFFF) { // Four bytes
        if (di + 3 >= destLimit) break;
        dest[di++] = 0xF0 + (codePoint >> 18);
        dest[di++] = 0x80 + ((codePoint >> 12) & 0x3F);
        dest[di++] = 0x80 + ((codePoint >> 6) & 0x3F);
        dest[di++] = 0x80 + (codePoint & 0x3F);
    } else if (codePoint <= 0x3FFFFFF) { // Five bytes
        if (di + 4 >= destLimit) break;
        dest[di++] = 0xF8 + (codePoint >> 24);
        dest[di++] = 0x80 + ((codePoint >> 18) & 0x3F);
        dest[di++] = 0x80 + ((codePoint >> 12) & 0x3F);
        dest[di++] = 0x80 + ((codePoint >> 6) & 0x3F);
        dest[di++] = codePoint & 0x3F;
    } else if (codePoint <= 0x7FFFFFFF) { // Six bytes
        if (di + 5 >= destLimit) break;
        dest[di++] = 0xFC + (codePoint >> 30);
        dest[di++] = 0x80 + ((codePoint >> 24) & 0x3F);
        dest[di++] = 0x80 + ((codePoint >> 18) & 0x3F);
        dest[di++] = 0x80 + ((codePoint >> 12) & 0x3F);
        dest[di++] = 0x80 + ((codePoint >> 6) & 0x3F);
        dest[di++] = codePoint & 0x3F;
    } else {
        // Not a code point... skip.
    }
}
dest[di] = 0;
return di;

}

这不是ndk 16和更低的问题。但是当我上升到ndk 17的时候，它会在下面造成错误。Android调试器在线显示

else if (codePoint <= 0x7FFFFFFF)

这是臭虫：

Error:(88, 30) error: comparison 'const int' <= 2147483647 is always true [-Werror,-Wtautological-constant-compare]

谢谢你的出席。

Answer 1

因为codePoint是一个int，所以它是一个有符号的32位数字。我猜想NDK r17是更严格的(可能是添加了-Wtautological-constant-compare -在发布说明中找不到)。

我认为您不需要使用int，而是需要使用unsigned int (可能是uint_least16_t，甚至uint_fast16_t)。还请参见http://en.cppreference.com/w/cpp/language/types (字符类型节)。