[This message was posted by Rolf Andersson of Pantor Engineering <[EMAIL 
PROTECTED]> to the "FAST Protocol" discussion forum at 
http://fixprotocol.org/discuss/46. You can reply to it on-line at 
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Jeff,

an ASCII string delta is represented on the wire by an integer followed by a 
string. The string is an SBIT-encoded value, so the length of the string can be 
deduced without a separate length entry.

The integer is interpreted as a subtraction length, ie. how many characters to 
remove from the previous value before inserting the string. The substraction 
length is represented as excess-1 when the value is negative (in order to 
express negative zero).

A few examples (1|"foo" means integer followed by string):

prev --- wire ---- value --- comment -----------------
""       0|"abc"   "abc"     remove 0 chars, add "abc" at end
"abc"    1|"a"     "aba"     remove 1 char, add "a" at end
"aba"    -1|"d"    "daba"    remove 0 chars, add "d" at front
"daba"   -3|"dc"   "dcba"    remove 2 chars, add "dc" at front

BTW, what's your company affiliation?

/Rolf


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