Rony:
Too many comparisons are being done from a performance perspective; a minimal
comparison for validation and no comparison for translation is the fastest.
Actual translation should be done with a pair of 256-byte arrays for speed AND
portability across character sets. Speed varies according to caching levels on
each chipset as compared to ANSI specific translation that can be accomplished
with just register operations. I will note that in some of my speed tests on a
commercial product using newer Intel chipsets, caching brings only the cache
lines of the trio of 256-byte tables used for translation into faster operation
than the register operations. In addition, both upper- and lower-case A-F are
handled with no performance impact.
static const char trinvalid[256] = {… invalid character table … }; //
0x00 for valid characters, non-zero for invalid characters
static const char trhigh [256] = {… high order nibble translations … };
static const char trlow [256] = {… low order nibble translations … };
{
char c1 = hexdata[i];
char c2 = hexdata[i+1];
if ((trinvalid[c1] | trinvalid[c2])) // Yes, the | symbol is correct to
drop to a single comparison operation
{
data[0] = 0x00;
return false;
}
data[dIdx++] = trhigh[c1] | trlow[c2];
i += 2;
}
Mark
From: Rony G. Flatscher <rony.flatsc...@wu.ac.at>
Sent: Thursday, April 18, 2019 9:04 AM
To: Open Object Rexx Developer Mailing List <oorexx-devel@lists.sourceforge.net>
Subject: [Oorexx-devel] An alternative algorithm for x2c()
While experimenting a little bit with C code to decode hex strings I came up
with the following code:
boolean hex2char(CSTRING hexData, size_t len, char *data)
{
if (len % 2 == 1) // not an even number of hex characters
{
data[0]='\0';
return false;
}
size_t dIdx=0;
for (size_t i=0; i<len; )
{
char tmp='\0';
switch (hexData[i++])
{
case '0': break;
case '1': tmp= 1; break;
case '2': tmp= 2; break;
case '3': tmp= 3; break;
case '4': tmp= 4; break;
case '5': tmp= 5; break;
case '6': tmp= 6; break;
case '7': tmp= 7; break;
case '8': tmp= 8; break;
case '9': tmp= 9; break;
case 'A': tmp=10; break;
case 'B': tmp=11; break;
case 'C': tmp=12; break;
case 'D': tmp=13; break;
case 'E': tmp=14; break;
case 'F': tmp=15; break;
default: // illegal character
data[0]='\0';
return false;
}
tmp<<=4; // shift to high order nibble
switch (hexData[i++])
{
case '0': break;
case '1': tmp |= 1; break;
case '2': tmp |= 2; break;
case '3': tmp |= 3; break;
case '4': tmp |= 4; break;
case '5': tmp |= 5; break;
case '6': tmp |= 6; break;
case '7': tmp |= 7; break;
case '8': tmp |= 8; break;
case '9': tmp |= 9; break;
case 'A': tmp |= 10; break;
case 'B': tmp |= 11; break;
case 'C': tmp |= 12; break;
case 'D': tmp |= 13; break;
case 'E': tmp |= 14; break;
case 'F': tmp |= 15; break;
default: // illegal character
data[0]='\0';
return false;
}
data[dIdx++]=tmp;
}
data[dIdx]='\0';
return true; // success
}
RexxRoutine1( RexxStringObject, cppX2C, CSTRING, hexData )
{
size_t len=strlen(hexData);
char *data=(char *) malloc (len+1);
boolean res=hex2char(hexData,len,data); // true, if translated; false, else
if (res==false)
{
free(data);
return NULLOBJECT; // for now: do not return a result, evoking a
runtime error
}
RexxStringObject rso=context->String(data, len/2);
free(data);
return rso;
}
Comparing the duration of x2c() with the above cppX2C() 1,000 times on a 512KB
string ( xrange("00"x,"FF"x)~copies(1000)~c2x ) the implementation of
hex2char() seems to be about 3,8 faster than x2c(). (This was tested on
Windows, 32-bit ooRexx.) Left the RexxRoutine1 cppX2C() in the above pasted
code, such that you could double-check it by merely copying and pasting the
above code and test it for yourself.
---rony
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