float_from_chars.cpp

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#include "parsers.hpp"
 
namespace parsers {
// this was copied from RapidJson (thanks RapidJson)
inline double pow_10(int n) {
    static double const e[] = {// 1e-0...1e308: 309 * 8 bytes = 2472 bytes
            1e+0, 1e+1, 1e+2, 1e+3, 1e+4, 1e+5, 1e+6, 1e+7, 1e+8, 1e+9, 1e+10, 1e+11, 1e+12, 1e+13, 1e+14, 1e+15, 1e+16, 1e+17, 1e+18,
            1e+19, 1e+20, 1e+21, 1e+22, 1e+23, 1e+24, 1e+25, 1e+26, 1e+27, 1e+28, 1e+29, 1e+30, 1e+31, 1e+32, 1e+33, 1e+34, 1e+35,
            1e+36, 1e+37, 1e+38, 1e+39, 1e+40, 1e+41, 1e+42, 1e+43, 1e+44, 1e+45, 1e+46, 1e+47, 1e+48, 1e+49, 1e+50, 1e+51, 1e+52,
            1e+53, 1e+54, 1e+55, 1e+56, 1e+57, 1e+58, 1e+59, 1e+60, 1e+61, 1e+62, 1e+63, 1e+64, 1e+65, 1e+66, 1e+67, 1e+68, 1e+69,
            1e+70, 1e+71, 1e+72, 1e+73, 1e+74, 1e+75, 1e+76, 1e+77, 1e+78, 1e+79, 1e+80, 1e+81, 1e+82, 1e+83, 1e+84, 1e+85, 1e+86,
            1e+87, 1e+88, 1e+89, 1e+90, 1e+91, 1e+92, 1e+93, 1e+94, 1e+95, 1e+96, 1e+97, 1e+98, 1e+99, 1e+100, 1e+101, 1e+102, 1e+103,
            1e+104, 1e+105, 1e+106, 1e+107, 1e+108, 1e+109, 1e+110, 1e+111, 1e+112, 1e+113, 1e+114, 1e+115, 1e+116, 1e+117, 1e+118,
            1e+119, 1e+120, 1e+121, 1e+122, 1e+123, 1e+124, 1e+125, 1e+126, 1e+127, 1e+128, 1e+129, 1e+130, 1e+131, 1e+132, 1e+133,
            1e+134, 1e+135, 1e+136, 1e+137, 1e+138, 1e+139, 1e+140, 1e+141, 1e+142, 1e+143, 1e+144, 1e+145, 1e+146, 1e+147, 1e+148,
            1e+149, 1e+150, 1e+151, 1e+152, 1e+153, 1e+154, 1e+155, 1e+156, 1e+157, 1e+158, 1e+159, 1e+160, 1e+161, 1e+162, 1e+163,
            1e+164, 1e+165, 1e+166, 1e+167, 1e+168, 1e+169, 1e+170, 1e+171, 1e+172, 1e+173, 1e+174, 1e+175, 1e+176, 1e+177, 1e+178,
            1e+179, 1e+180, 1e+181, 1e+182, 1e+183, 1e+184, 1e+185, 1e+186, 1e+187, 1e+188, 1e+189, 1e+190, 1e+191, 1e+192, 1e+193,
            1e+194, 1e+195, 1e+196, 1e+197, 1e+198, 1e+199, 1e+200, 1e+201, 1e+202, 1e+203, 1e+204, 1e+205, 1e+206, 1e+207, 1e+208,
            1e+209, 1e+210, 1e+211, 1e+212, 1e+213, 1e+214, 1e+215, 1e+216, 1e+217, 1e+218, 1e+219, 1e+220, 1e+221, 1e+222, 1e+223,
            1e+224, 1e+225, 1e+226, 1e+227, 1e+228, 1e+229, 1e+230, 1e+231, 1e+232, 1e+233, 1e+234, 1e+235, 1e+236, 1e+237, 1e+238,
            1e+239, 1e+240, 1e+241, 1e+242, 1e+243, 1e+244, 1e+245, 1e+246, 1e+247, 1e+248, 1e+249, 1e+250, 1e+251, 1e+252, 1e+253,
            1e+254, 1e+255, 1e+256, 1e+257, 1e+258, 1e+259, 1e+260, 1e+261, 1e+262, 1e+263, 1e+264, 1e+265, 1e+266, 1e+267, 1e+268,
            1e+269, 1e+270, 1e+271, 1e+272, 1e+273, 1e+274, 1e+275, 1e+276, 1e+277, 1e+278, 1e+279, 1e+280, 1e+281, 1e+282, 1e+283,
            1e+284, 1e+285, 1e+286, 1e+287, 1e+288, 1e+289, 1e+290, 1e+291, 1e+292, 1e+293, 1e+294, 1e+295, 1e+296, 1e+297, 1e+298,
            1e+299, 1e+300, 1e+301, 1e+302, 1e+303, 1e+304, 1e+305, 1e+306, 1e+307, 1e+308};
    return e[n];
}
 
bool float_from_chars(char const* start, char const* end, float& float_out) { // returns true on success
    // first read the chars into an int, keeping track of the magnitude
    // multiply by a pow of 10
 
    int32_t magnitude = 0;
    int64_t accumulated = 0;
    bool after_decimal = false;
 
    if(start == end) {
        float_out = 0.0f;
        return true;
    }
 
    bool is_negative = false;
    if(*start == '-') {
        is_negative = true;
        ++start;
    } else if(*start == '+') {
        ++start;
    }
 
    for(; start < end; ++start) {
        if(*start >= '0' && *start <= '9') {
            accumulated = accumulated * 10 + (*start - '0');
            magnitude += int32_t(after_decimal);
        } else if(*start == '.') {
            after_decimal = true;
        } else {
            // maybe check for non space and throw an error?
        }
    }
    if(!is_negative) {
        if(magnitude > 0)
            float_out = float(double(accumulated) / pow_10(magnitude));
        else
            float_out = float(accumulated);
    } else {
        if(magnitude > 0)
            float_out = -float(double(accumulated) / pow_10(magnitude));
        else
            float_out = -float(accumulated);
    }
    return true;
}
 
bool double_from_chars(char const* start, char const* end, double& dbl_out) { // returns true on success
    int32_t magnitude = 0;
    int64_t accumulated = 0;
    bool after_decimal = false;
 
    if(start == end) {
        dbl_out = 0.0;
        return true;
    }
 
    bool is_negative = false;
    if(*start == '-') {
        is_negative = true;
        ++start;
    } else if(*start == '+') {
        ++start;
    }
 
    for(; start < end; ++start) {
        if(*start >= '0' && *start <= '9') {
            accumulated = accumulated * 10 + (*start - '0');
            magnitude += int32_t(after_decimal);
        } else if(*start == '.') {
            after_decimal = true;
        } else {
        }
    }
    if(!is_negative) {
        if(magnitude > 0)
            dbl_out = double(accumulated) / pow_10(magnitude);
        else
            dbl_out = double(accumulated);
    } else {
        if(magnitude > 0)
            dbl_out = -double(accumulated) / pow_10(magnitude);
        else
            dbl_out = -double(accumulated);
    }
    return true;
}
} // namespace parsers