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While searching the web for fast i/o in c++, this is the "best" (according to me) that I have come across

#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
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;
};

int main()
{
    ;
}

But, it was nothing written about how to take input or give output.

It would be of great help, if you can tell how to take input a integer and a c++ string and give output, with an example.

acpurt
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    You realise that your I/O time will be dominated by the actual I/O, not the conversion from string to int? – Oliver Charlesworth Jan 01 '13 at 16:20
  • I didn't get your question. I am a beginner. – acpurt Jan 01 '13 at 16:26
  • Do you need to read and write your data in text or in binary form? Can your data be easily serialized in primitive values? Whatever the answers to these questions are: FastInput and FastOutput are very unlikely to meet your requirements, e.g. it doesn't support reading and writing strings. – Codo Jan 01 '13 at 16:26
  • @acpurt, he means that the I/O time depends on how fast the system itself can transfer the data, not by the conversion from a string to a integer. – Rivasa Jan 01 '13 at 16:28
  • @Link: I meant more the time taken by the system to transfer the data to/from the console/file/whatever. – Oliver Charlesworth Jan 01 '13 at 16:29
  • @Codo ok, then can you give example for int. – acpurt Jan 01 '13 at 16:30
  • @OliCharlesworth I need this for online judges, as runtime is very crucial there. – acpurt Jan 01 '13 at 16:33
  • @Oli: Nice assumption. Widespread assumption. But test it, on many systems that is NOT TRUE. http://stackoverflow.com/q/4340396/103167 – Ben Voigt Jan 01 '13 at 17:01
  • You do realize that IO is already buffered. So you just re-invented the wheel. The difference is that you put a fixed size wheel on all systems while most standard libraries have a custom sized wheel for the system they were designed for. – Martin York Jan 01 '13 at 17:08

1 Answers1

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The following code reads an unsigned integer value from standard input:

FastInput fi;
uint32_t value = fi.ReadNext();

To write an unsigned integer value to standard output:

FastOutput fo;
fo.PrintUint(123456, '\n');
fo.Flush();

But seriously: Forget about these classes. I cannot image how this class could be in any way useful for whatever you're trying to achieve.

Codo
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