CODEWITHSUNDEEP
php
user1062893
user1062893

Reputation: 89

what is the maximum number limit for base_convert() function?

I would like to use base_convert function to convert 60 bit binary data to Hex code as follows. But the result is not correct. The output of the code below is 4e08556312ffc00 but the correct output is 4E08556312FFBFF. Can anybody tell me why? is 60 bit too large to the function? 

echo "The beacon ID in Hexadecimal is".base_convert
         ("010011100000100001010101011000110001001011111111101111111111",2, 16);

Thank

Upvotes: 1

Views: 5038

Answers (4)

danorton
danorton

Reputation: 12015

It is the larger of:

  1. PHP_INT_MAX and
  2. The maximum of the contiguous set of integers that can be expressed as a float.

Typical PHP implementations use IEEE 754 for implementing floating point numbers, which has a 53-bit significand, so the typical limit for 32-bit environments is 2⁵³ (0x20000000000000) and for 64-bit environments, the limit is 2⁶³-1 (0x7fffffffffffffff).

There’s a trivial solution if you have the PHP gmp extension ( http://php.net/gmp ):

$hexNumber = gmp_strval( gmp_init( $binNumber, 2 ), 16 ) ;

If you have the bc extension (http://php.net/bc ), my (free & open source) WeirdoCustomDigits module will do conversions with arbitrary bases and arbitrary digit characters, without limitation.

If you're simply converting between base 2 and base 16, as with your example, you can get by without bc or gmp. See the source in the WeirdoCustomDigits module for WeirdoCustomDigits::binFromHex() and WeirdoCustomDigits::hexFromBin().

Upvotes: 0

user2560436
user2560436

Reputation: 1

My tests reveal a loss of precision over 43bits.

I work on a Win XP base + easyphp 3.1.81 with default settings.

I use this base_convert for a genealogical application, and the limit of 43 generations is - sometimes - not enough.

Upvotes: 0

Jon
Jon

Reputation: 437474

I have posted an implementation of a base conversion function without such limits in my answer to another question here.

Upvotes: 2

zessx
zessx

Reputation: 68810

According to base_convert and floating numbers documentation, base_convert will lose precision on large numbers.

Instead of, you can use bin2hex, which is not limited (this function use and return strings)

Upvotes: 0

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