Make CSV table of GMP options behavior in PHP

<?php
$posN = gmp_init(0x0123456789ABCDEF);
$negN = gmp_init(-0x0123456789ABCDEF);

/**
 * A function to test the behavior of GMP given various bitfield options
 * @boolean $sign determines whether a positive or negative number is used
 * @boolean $word_size is the size of the word passed to gmp_export
 * @boolean $signifigant_w determine whether w is most significant or least signifigant
 * @boolean $endianness is whether big endian or little endian.
 *
 * @return string the calculated and formatted result of the options
 */
function testGmpBehavior($sign, $word_size, $signifigant_w, $endianness) {
    global $posN, $negN;
    $num = $sign ? $posN : $negN;
    $sig = $signifigant_w ? GMP_MSW_FIRST : GMP_LSW_FIRST;
    $endian = $endianness ? GMP_LITTLE_ENDIAN : GMP_BIG_ENDIAN;
    $hex = bin2hex(gmp_export($num, $word_size, $sig | $endian));
    $chunked = strtoupper( chunk_split($hex, 2*$word_size, "_") );
    return substr($chunked, -1) === "_" ? substr($chunked, 0, -1) : $chunked;
}
echo "Sign,Word Size,Sig,Endian,gmp_export Hex Result", PHP_EOL;
for ($sign=1; 0 <= $sign; $sign--)
    for ($wSize=1; $wSize <= 8; $wSize++)
        for ($sigW=1; 0 <= $sigW; $sigW--)
            for ($end=1; 0 <= $end; $end--) {
                echo !!$sign ? "+pos" : "-neg", ",";
                echo $wSize, " bytes", ",";
                echo !!$sigW ? "MSW" : "LSW", ",";
                echo !!$end ? "little" : "big", ",";
                echo testGmpBehavior(!!$sign, $wSize, !!$sigW, !!$end);
                echo PHP_EOL;
            }