Function to unwrap scientific notation into float number. Made with PHP 8.4.3.

unwrapE.php

<?php

function unwrapE(float $value)
{
    $strVal = strval($value);
    
    if (!str_contains($strVal, 'E')) {
        return $strVal;
    }
    
    [$beforeE, $afterE] = explode('E', $strVal);
    [$beforeEBeforeDot, $beforeEAfterDot] = explode('.', $beforeE);
    
    if ($beforeEAfterDot === '0') {
        $beforeEAfterDot = '';
    }
    
    $e = intval($afterE);
    if ($e < 0) {
        $resultZeroPadLen = strlen($beforeEAfterDot) + abs($e);
        
        $result = str_pad($beforeEBeforeDot . $beforeEAfterDot, $resultZeroPadLen + 1, '0', STR_PAD_LEFT);
        $result = substr_replace($result, '.', strlen($result) - $resultZeroPadLen, 0);
    } else {
        $resultZeroPadLen = $e;
        
        $result = str_pad($beforeEAfterDot, $resultZeroPadLen, '0', STR_PAD_RIGHT);
        $trailing = strlen($result) - $resultZeroPadLen;
        
        if ($trailing < 0) {
            $result = substr_replace($result, '.', $trailing, 0);
        }
        
        $result = $beforeEBeforeDot . $result;
    }
    
    return $result;
}

assert(unwrapE(1.25E-15) === '0.00000000000000125');
assert(unwrapE(221.25E-15) === '0.00000000000022125');
assert(unwrapE(0.25E-15) === '0.00000000000000025');
assert(unwrapE(0.253E-15) === '0.000000000000000253');
assert(unwrapE(123456789.25E-8) === '1.2345678925');
assert(unwrapE(1E-30)   === '0.000000000000000000000000000001');
assert(unwrapE(0.1E-30) === '0.0000000000000000000000000000001');

assert(unwrapE(0.5E30) === '500000000000000000000000000000');
assert(unwrapE(0.5E+31) === '5000000000000000000000000000000');
assert(unwrapE(5.1E+30) === '5100000000000000000000000000000');
assert(unwrapE(2.5123456789123E+17) === '251234567891230000');