1. RE: Changing data types Concluded
> -----Original Message-----
> From: Allen Robnett [mailto:alrobnett at alumni.princeton.edu]
> Subject: Changing data types Concluded
>
>
>
> Derek wrote:
>
> <<Yes, it was a rather salient point as we all assumed you
> were using standard
> Euphoria code to read and search the file. Using the API and
> raw ram buffers
> instead changes things a lot, as we are no longer talking
> about atoms and
> sequences.
> Derek >>
>
>
> Sorry about the confusion. I am a math teacher, not a
> programmer, and I learn the lingo by having programmers kick
> me when I make a mistake.
No problem.
> Back to my original question.
> I am reading a 200MB text file into a preallocated buffer via
> an API method suggested by Euman. The file consists of 2^24
> fixed length fields, each 12 bytes long. I would like to take
> advantage of EU's features to the greatest extent possible in
> searching the file. I am currently doing this by successively
> peeking at the first 4 characters of each field and telling
> EU that they represent an unsigned integer (actually an atom).
>
> The search of the 16,777,216 fields is done in 6.6 seconds if
> "not equal()" is used, and in 5.8 seconds if != is used. The
> latter is possible because the 4-character sub-field is
> treated as an integer.
>
> Questions:
> 1. Does anyone see a way to improve on this time?
Yes. See below.
> 2. Could I also arrange to use an 8-byte sub-field?
As you have all the bytes in RAM, you do not have to convert them to
Euphoria integers etc... You can use the RAM-based string searching routines
built in to Windows.
integer kernel32
integer CompareString
kernel32 = open_dll("kernel32.dll")
CompareString = define_c_func(kernel32, "CompareStringA",
{C_UINT,C_UINT,C_UINT,C_INT,C_UINT,C_INT},C_INT)
And assuming you have the file loaded into RAM at the address stored in
'RAMADDR' then you can do
constant CSTR_ERROR = 0
constant CSTR_LESS_THAN = 1
constant CSTR_EQUAL = 2
constant CSTR_GREATER_THAN = 3
atom FindStr
integer offset
atom result
integer len
constant recsize = 12
sequence TheRecord
-- Find first text record that begins with 'abcd'.
FindStr = allocate_string("abcd")
len = 4
offset = 0
while offset < FileSize do
result = c_func(CompareString,{0, 0, RAMADDR+offset, len, FindStr, len})
if result = CSTR_ERROR or result = CSTR_EQUAL then
exit
end if
offset += recsize
end while
-- Copy the whole record into a sequence
TheRecord = peek({RAMADDR+offset, recsize})
> 3. Is there some way to persuade EU "position()" to allow the
> display line to be greater than 24 (using vanilla DOS)?
integer maxlines
maxlines = text_rows(50) --Values of 25, 28, 43 and 50 lines are supported
by most video cards.
--
Derek
