我见过有人使用这个 FastInput 类来提高他们的编译时间，但是我无法清楚地理解它里面的功能。我的问题是：我需要学习什么来理解这些功能，以及这个类如何提高整体时间。如果有人可以解释这个类中的功能以及它们做什么或至少请提供一些好的参考，这将是有帮助的。
class FastInput {
public:
FastInput() {
m_dataOffset = 0;
m_dataSize = 0;
m_v = 0x80000000;
}
uint32_t ReadNext() {
if (m_dataOffset == m_dataSize) {
int r = read(0, m_buffer, sizeof(m_buffer));
if (r <= 0) return m_v;
m_dataOffset = 0;
m_dataSize = 0;
int i = 0;
if (m_buffer[0] < '0') {
if (m_v != 0x80000000) {
m_data[m_dataSize++] = m_v;
m_v = 0x80000000;
}
for (; (i < r) && (m_buffer[i] < '0'); ++i);
}
for (; i < r;) {
if (m_buffer[i] >= '0') {
m_v = m_v * 10 + m_buffer[i] - 48;
++i;
} else {
m_data[m_dataSize++] = m_v;
m_v = 0x80000000;
for (i = i + 1; (i < r) && (m_buffer[i] < '0'); ++i);
}
}
}
return m_data[m_dataOffset++];
}
public:
uint8_t m_buffer[32768];
uint32_t m_data[16384];
size_t m_dataOffset, m_dataSize;
uint32_t m_v;
};
class FastOutput {
public:
FastOutput() {
m_dataOffset = 0;
}
~FastOutput() {
}
void Flush() {
if (m_dataOffset) {
if (write(1, m_data, m_dataOffset));
m_dataOffset = 0;
}
}
void PrintUint(uint32_t v, char d) {
if (m_dataOffset + 11 > sizeof(m_data)) Flush();
if (v < 100000) {
if (v < 1000) {
if (v < 10) {
m_data[m_dataOffset + 0] = v + 48;
m_dataOffset += 1;
} else if (v < 100) {
m_data[m_dataOffset + 1] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 0] = v + 48;
m_dataOffset += 2;
} else {
m_data[m_dataOffset + 2] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 1] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 0] = v + 48;
m_dataOffset += 3;
}
} else {
if (v < 10000) {
m_data[m_dataOffset + 3] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 2] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 1] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 0] = v + 48;
m_dataOffset += 4;
} else {
m_data[m_dataOffset + 4] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 3] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 2] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 1] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 0] = v + 48;
m_dataOffset += 5;
}
}
} else {
if (v < 100000000) {
if (v < 1000000) {
m_data[m_dataOffset + 5] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 4] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 3] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 2] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 1] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 0] = v + 48;
m_dataOffset += 6;
} else if (v < 10000000) {
m_data[m_dataOffset + 6] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 5] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 4] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 3] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 2] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 1] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 0] = v + 48;
m_dataOffset += 7;
} else {
m_data[m_dataOffset + 7] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 6] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 5] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 4] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 3] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 2] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 1] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 0] = v + 48;
m_dataOffset += 8;
}
} else {
if (v < 1000000000) {
m_data[m_dataOffset + 8] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 7] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 6] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 5] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 4] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 3] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 2] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 1] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 0] = v + 48;
m_dataOffset += 9;
} else {
m_data[m_dataOffset + 9] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 8] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 7] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 6] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 5] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 4] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 3] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 2] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 1] = v - v / 10 * 10 + 48; v /= 10;
m_data[m_dataOffset + 0] = v + 48;
m_dataOffset += 10;
}
}
}
m_data[m_dataOffset++] = d;
}
void PrintChar(char d) {
if (m_dataOffset + 1 > sizeof(m_data)) Flush();
m_data[m_dataOffset++] = d;
}
void ReplaceChar(int offset, char d) {
m_data[m_dataOffset + offset] = d;
}
public:
uint8_t m_data[32768];
size_t m_dataOffset;
};
FastInput g_fi;
FastOutput g_fo;