Convert number/integer/float into string without exponential notation

number_to_string.php

<?php

declare(strict_types=1);

function numberToString($number, $precision = null)
{
    if (is_int($number)) {
        return (string) $number;
    }
    
    if ($precision === null) {
        $precision = (int) ini_get('precision');
    }
    
    $sign = '';
    $number = sprintf('%.' . ($precision - 1) . 'e', (float) $number);
    if ($number[0] === '-') {
        $sign = '-';
        $number = substr($number, 1);
    }
    
    if ($number[1] !== '.') {
        throw new InvalidArgumentException(
            sprintf('Unable to convert "%s" into a string representation.', $number)
        );
    }

    $number = explode('e', $number);
    $digits = rtrim($number[0][0] . substr($number[0], 2), '0');
    $shift = (int) $number[1] + 1;
    
    if ($shift < 1) {
        $result = '0.'.str_repeat('0', ($shift) * -1).$digits;
    }
    elseif (strlen($digits) <= $shift) {
        $result = str_pad($digits, $shift, '0');
    }
    else {
        $result = substr($digits, 0, $shift).'.'.substr($digits, $shift);
    }
    
    return $sign.$result;
}

alternative:

<?php

declare(strict_types=1);

function numberToString(float $number, ?int $precision = null)
{
    if ($precision === null) {
        $precision = (int) ini_get('precision');
    }
    
    if (!preg_match(
        '/^(-?)(\d)\.(\d+)e([+-]\d+)$/',
        sprintf('%.' . ($precision - 1) . 'e', (float) $number), 
        $match
    )) {
        throw new InvalidArgumentException(
            sprintf('Unable to convert "%s" into a string representation.', $number)
        );
    }

    $digits = rtrim($match[2] . $match[3], '0');
    $shift = (int) $match[4] + 1;
    
    return $match[1] . rtrim(
        (substr(str_pad($digits, $shift, '0'), 0, max(0, $shift)) ?: '0')
            . '.' . str_repeat('0', max(0, -$shift))
            . substr($digits, max(0, $shift)),
        '.'
    );
}

echo numberToString(0.0) . "\n";
echo numberToString(-0.0) . "\n";
echo numberToString(1.0) . "\n";
echo numberToString(-1.0) . "\n";
echo numberToString(0.1) . "\n";
echo numberToString(0.1 + 0.2 + 0.1 + 0.2) . "\n";
echo numberToString(0.066) . "\n";
echo numberToString(0.0000000000000000000000000000000000000000000000000000001) . "\n";
echo numberToString(1.0) . "\n";
echo numberToString(1.1) . "\n";
echo numberToString(10000000.0) . "\n";
echo numberToString(10000000.1) . "\n";
echo numberToString(10000000.01) . "\n";
echo numberToString(1234567890123456789012345678901234567890123456789012345678901234567890) . "\n";
echo numberToString(PHP_INT_MAX) . "\n";
echo numberToString(9000000000000000000) . "\n";
echo numberToString(9000000000000000000.0) . "\n";
echo numberToString((float)PHP_INT_MAX) . "\n";
echo numberToString(4503599627370496) . "\n";
echo numberToString(4503599627370496.0) . "\n";
echo numberToString(1.2345678901234567890123456789) . "\n";
echo (string) 1.2345678901234567890123456789 . "\n";
echo numberToString(PHP_INT_MAX * PHP_INT_MAX) . "\n";
echo numberToString(PHP_FLOAT_EPSILON) . "\n";
echo numberToString(0.001+PHP_FLOAT_EPSILON) . "\n";
echo numberToString(PHP_FLOAT_MIN) . "\n";
echo numberToString(PHP_FLOAT_MAX) . "\n";
#echo numberToString(INF) . "\n";
#echo numberToString(NAN) . "\n";