有没有办法在PHP中获取浮点数的二进制表示?类似Java的Double.doubleToRawLongBits()。
给定一个正的浮点数,我想获得最大的可表示浮点数,该数字小于该数。在Java中,我可以这样做:
double x = Double.longBitsToDouble(Double.doubleToRawLongBits(d) - 1);
但我在PHP中没有看到任何类似内容。
答案 0 :(得分:4)
这是我使用Peter Bailey的建议提出的解决方案。它需要64位版本的PHP。我并不认为这是生产质量的任何方式,但我分享以防任何人想要建立它。 (事实上,在我发布问题之后,我最终完成了一些不同的事情,但我把它留在这里作为一项智力练习。)
// Returns the largest double-precision floating-point number which
// is less than the given value. Only works for positive values.
// Requires integers to be represented internally with 64 bits (on Linux
// this usually means you're on 64-bit OS with PHP built for 64-bit OS).
// Also requires 64-bit double-precision floating point numbers, but I
// think this is the case pretty much everywhere.
// Returns false on error.
function prevDouble($d) {
$INT32_MASK = 0xffffffff;
if((0x1deadbeef >> 32) !== 1) {
echo 'error: only works on 64-bit systems!';
return false;
}
if($d <= 0) {
return false;
}
$beTest = bin2hex(pack('d', 1.0)); //test for big-endian
if(strlen($beTest) != 16) {
echo 'error: system does not use 8 bytes for double precision!';
return false;
}
if($beTest == '3ff0000000000000') {
$isBE = true;
}
else if($beTest == '000000000000f03f') {
$isBE = false;
}
else {
echo 'error: could not determine endian mode!';
return false;
}
$bin = pack('d', $d);
//convert to 64-bit int
$int = 0;
for($i = 0; $i < 8; $i++)
$int = ($int << 8) | ord($bin[$isBE ? $i : 7 - $i]);
$int--;
//convert back to double
if($isBE)
$out = unpack('d', pack('N', ($int >> 32) & $INT32_MASK) . pack('N', $int & $INT32_MASK));
else
$out = unpack('d', pack('V', $int & $INT32_MASK) . pack('V', ($int >> 32) & $INT32_MASK));
return $out[1];
}
答案 1 :(得分:3)
作为一个额外的答案,不是整个问题,而是标题:
如果你想看看你的花车看起来像二进制文件:
function floatToBinStr($value) {
$bin = '';
$packed = pack('d', $value); // use 'f' for 32 bit
foreach(str_split(strrev($packed)) as $char) {
$bin .= str_pad(decbin(ord($char)), 8, 0, STR_PAD_LEFT);
}
return $bin;
}
echo floatToBinStr(0.0000000000000000000000000000000000025).PHP_EOL;
echo floatToBinStr(0.25).PHP_EOL;
echo floatToBinStr(0.5).PHP_EOL;
echo floatToBinStr(-0.5).PHP_EOL;
输出:
0011100010001010100101011010010110110111111110000111101000001111
0011111111010000000000000000000000000000000000000000000000000000
0011111111100000000000000000000000000000000000000000000000000000
1011111111100000000000000000000000000000000000000000000000000000
答案 2 :(得分:2)
这不是一个完整的答案,但我知道将浮动放入二进制文件的唯一方法是使用pack()
答案 3 :(得分:0)
的java:
long lnBits = Double.doubleToLongBits(longValue);
Byte[] bits = new byte [] {
(byte) ((value << 56) >>> 56),
(byte) ((value << 48) >>> 56),
(byte) ((value << 40) >>> 56),
(byte) ((value << 32) >>> 56),
(byte) ((value << 24) >>> 56),
(byte) ((value << 16) >>> 56),
(byte) ((value << 8) >>> 56),
(byte) (value >>> 56)}
PHP:
$bits = $bitsFromJava;
$str="";
for($i=0;$i<8;i++){
$str.=chr($bits[$i]);
}
$longValue=unpack('d',$str);
$bitsToJava=array();
for(str_split(pack($longValue)) as $chr){
$bitsToJava[]=ord($chr);
}