Conversion error on large number (> 32bit)

[pauldeng]

Hi all,

Firstly, I like to appreciate the author for this lib. Understand it is the most downloaded lib for this function and has been stable for years.

Maybe I missed out something obvious, can someone in the community tell me what happens here:

// tested on nodejs v14, v18
const sprintf = require('sprintf-js');

let num = 150460469257; // 0x2308249009

// simpliy convert number to hex string

const hexStr_native = num.toString(16);
const hexStr_sprintfjs = sprintf.sprintf("%x", num);

console.log(hexStr_native);    // 2308249009 as expected
console.log(hexStr_sprintfjs); // expecting 2308249009, but get 8249009. Seems only max 4 bytes (32 bit) number allowed, larger than that will be trimmed. I am not aware this lib has this restriction.

Thanks.

Cheers,
Paul

[alexei]

I believe that happens because the library uses the right shift operator to ensure the number is positive:

sprintf.js/src/sprintf.js

Lines 114 to 116 in 8a3a4bb

	case 'x':
	arg = (parseInt(arg, 10) >>> 0).toString(16)
	break

In doing so, the value is converted to a 32 bits integer. But 150460469257 is greater than the largest 32-bits integer, signed or unsigned, so I guess it overflows.

I don't think I've ever thought of a use for hexadecimal notation beyond representing colors. In such cases 32 bits are sufficient. However, this limitation of the library seems like an unfortunate accident and a bug.

[pauldeng]

Thanks for your reply.

Perhaps %x, %lX can be introduced, just like how C handles long type.

Cheers,
Paul

[alexei]

Wouldn't you say it would be better to use Math.abs to ensure the value is positive, instead of introducing features which are particular to C but strange to JS?