Need Tcl help: Convert to ulong

[Rentian Huang]

I have a C function that generates a key, and needs to be converted into a Tcl function:

Code:

void sum_add(ulong*sum, const char* str)
{
 size_t len = strlen(str);
 for (size_t i=0; i

This is what I did:

Code:

proc sum_add {sum str} {
set len [string length $str]
for {set i 0} {$i < $len} {incr i} { set sum 0 set sum [expr ($sum + ([scan [string index $str $i] %c] * (($i + 1) << 4))) % 0x10000] } return $sum }

ulong is a 32-bit unsigned integer

The correct result is: [sum_add 0 “Dr.X”] = 0x00003120

But I got [sum_add 0 “Dr.X”] = 5632

Why? I guess the scan has problem but I don’t know how to fix it.

Can anyone help? Thanks!

Sam   8)

Topic

[John Mercogliano]

Rentian,

  You’re going to kick yourself but the first thing you need to do is move the set sum 0 outside of the for loop.  That will fix it so that it will return the correct integer value. Expr always returns a numeric result so something like expr 0x21 * 0x02 returns 66 instead of 0x42. You will need to use the format command to return a Hex string as so:

set sum [format 0x%08x [expr ($sum + ([scan [string index $str $i] %c] * (($i + 1) << 4))) % 0x10000]]

John Mercogliano
Sentara Healthcare
Hampton Roads, VA

[Rentian Huang]

John, you are absolutely right, I was being stupid putting that [set sum 0] in the loop, and your format 0x%08x works fine too.

But somehow I just can not get the correct result. I changed my code as below:

Code:

proc sum_add {sum str} {
set len [string length $str]
for {set i 0} {$i < $len} {incr i} { set char [string index $str $i] if { ![string is integer $char] } { set char [scan $char %c] } set sum [format 0x%08x [expr ($sum + ($char * (($i + 1) << 4))) % 0x10000]] } return $sum }

This is the calls:

Code:

set sum 0
set sum [sum_add $sum “”]
set sum [sum_add $sum “”]
set sum [sum_add $sum “Dr.X”]
echo sum_char<$sum>
set sum [sum_add $sum 1065507963]
echo sum_num<$sum>

This is the output:

Code:

sum_char<0x00003120>
sum_num<0x000041f0>

And according to our vendor, the first one is correct, but the 2nd has problem:

Code:

sum in 1st step: 0x00003120
sum in 2nd step: 0x0000e6f0

Thanks for any more help, I have been struggling for this for a while   😥

Sam

[John Mercogliano]

Code:

proc sum_add {sum str} {
  set len [string length $str]
  for {set i 0} {$i < $len} {incr i} {      set char [string index $str $i]      set char [scan $char %c]      set sum [format 0x%08x [expr ($sum + ($char * (($i + 1) << 4))) % 0x10000]]   }   return $sum }

Notice I removed the if statement? Did you try it this way?  Looking at your C code, the if logic is not needed as even if the string contains a number the C code was still using the ascii equivalent in its calculations not the actual number.  So for example “1065507963”, char would be equal to 42 not 1, 48 not 0…etc

Hope this helps.

John Mercogliano
Sentara Healthcare
Hampton Roads, VA

[Rentian Huang]

That works like magic, John, thanks so much for the help, I really appreciate it!!!

Sam  😀

[Author]

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