641279 - potential performance waste caused by sprintf

Status: RESOLVED WONTFIX

(NSS :: Libraries, defect, P5)

Description

[Ce Zhang]

User-Agent:       Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.9.2.15) Gecko/20110303 Firefox/3.6.15
Build Identifier: potential performance waste caused by sprintf

/firefox-4.0b11.source/security/nss/cmd/lib/secutil.c:4111
           sprintf(dst, "%02x", *src++);
/firefox-4.0b11.source/security/nss/cmd/certutil/certutil.c:776
           sprintf(dst, "%02x", *src++);

After reading mozilla codes, I find these two code fragments. Using this method to convert a number into a string which represents the related hex number is very slow.

This is a patch:

static void array_to_hex( char * to , const char * str , unsigned char  len )
{
    const char * str_end = str + len;
    for( ; str != str_end ; ++ str )
    {
       *to++ = _dig_vec_lower[ ((unsigned char) *str) >> 4 ];
       *to++ = _dig_vec_lower[ ((unsigned char) *str) & 0x0F ];
    }
}

In my unit test, my patch run as 7 times faster as these two code fragments I find. If these two code fragments will be executed many times, I believe it can slow down the whole application. 

I suggest that we should fix these two bugs. 


Reproducible: Always

Steps to Reproduce:
1.code review
2.
3.

Comment 1

[Ludovic Hirlimann [:Usul]]

Ce Zhang, can you provide a proper patch against the current trunk cvs ?

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