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Best way to read a negative number from a byte stream?
by Ben Weaver 12 Aoû '09

12 Aoû '09

Hi all, I'm implementing Google's protocol buffers in Gambit-C. One of the basic data types is a "varint" which represents a 64-bit integer as a variable number of bytes in a byte stream. This is the first time I've tried to "decode" data from a byte stream as a signed number in Scheme. In other programming languages that don't have bignums I would have relied on integer overflow and done something like: `(+ 1 (bitwise-not value))'. Has anyone else tried to do something like this before? Is there a better way? I fiddled around with various approaches and ended up with this: (define (negative-64bit-value value) (copy-bit-field 63 0 value -1)) Which is used in the following way: ;; This value was accumulated by folding bytes from a stream into an ;; accumulator. The seed value was zero and each byte was added to ;; the accumulator after being aligned by ARITHMETIC-SHIFT. It is not ;; known whether the value should be positive or negative until the ;; last byte in the sequence is read from the stream. (define accumulated-value #x7fffffffffffffffffff) ;; => 604462909807314587353087 (negative-64bit-value accumulated-value) ;; => -1 Thanks, -Ben

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gambit application
by francesco bracchi 11 Aoû '09

11 Aoû '09

I've just put online http://notapipe.net. It is a realtime collaborative text editor, and all the server side part is written in gambit-c. I want to thank Mark Feeley and all the gambit community, for creating and maintaining Gambit-C system. francesco.

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Hashing of types
by Alex Queiroz 10 Aoû '09

10 Aoû '09

Hallo, Is there a way to tell the table hashing function to ignore a field of a define-type'd value? I am writing a function for alpha-beta searching, and I'd like to use a cache to avoid re-searching previously calculated positions. So I have defined the type: (define-type node id: d7aba792-963c-41c9-b1fd-e5e26590ab34 seq ply move value ; cached value of evaluation function, ; not full search value (board unprintable:)) I need that the field 'move' be ignored by the hash function for equal?. Is that possible? Cheers, -- -alex http://www.ventonegro.org/

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Unsubscribing
by Derek Peschel 09 Aoû '09

09 Aoû '09

Thanks, Marc and everyone else, for working on Gambit and discussing it. Unfortunately the list traffic is too great for me right now and I will be unsubscribing later today. Can someone else take over the "Release notes" page on the wiki? I created it because I wanted information about the history of Gambit in one place, wanted to advertise serious "don't use this release" bugs, and wanted to know which parts of Gambit were changing. The page doesn't answer the last question yet, but it does answer the first two. With a little bit of work on each new release, I think the page will continue to be as useful as it is now (however useful that is). -- Derek

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maco to call define w/ varaible name created dynamically
by lowly coder 09 Aoû '09

09 Aoû '09

Suppose I have the following: (define global "foo") (define-macro (magic ...)) (magic "bar" 1); <-- I want this to expand to (define foo-bar 1) How can I make this happen? The macro needs to access the value of "global", but it can't at compile time; if the macro outputs some code that takes advantage of things at run time, I can get to: (define (string->symbol (string-append "foo" "-" "bar")) 1) but this, of course, tries to define a function string->symbol rather than what I want. Thanks!

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Compiling GSI on windows with ___SHARED defined
by Ivan Kelly 08 Aoû '09

08 Aoû '09

Im compiling gambit on windows with ___SHARED defined, in a symbian OS emulator environment. I've managed to get it working without issue compiling to one big monolith, taking pointers from the openwatcom batch file (also compiled with gcce and running on phone). However, ___SHARED is proving to be a bit more difficult. The dll compiles with very little issue. ___LIBRARY and ___PRIMAL are defined for all *.c inputs to that, and it compiles without error apart from the unused variables, whose warnings i've hidden. gsi is proving trickier though. In getting a load of errors for ___gstate being defined in many places. Also, ___G__20__gsilib is twice defined. <snip> mwldsym2.exe: Multiply defined symbol: struct ___global_state_struct ___gstate (?___gstate@@3U___global_state_struct@@A) in mwldsym2.exe: files _gambcgsi.o, _gsilib.o mwldsym2.exe: Multiply defined symbol: struct ___glo_struct ___G__20___gsilib (?___G__20___gsilib@@3U___glo_struct@@A) in mwldsym2.exe: files _gambcgsi.o, _gsilib.o mwldsym2.exe: Multiply defined symbol: struct ___global_state_struct ___gstate (?___gstate@@3U___global_state_struct@@A) in mwldsym2.exe: files _gsi.o, _gsilib.o mwldsym2.exe: Multiply defined symbol: struct ___global_state_struct ___gstate (?___gstate@@3U___global_state_struct@@A) in mwldsym2.exe: files _gsi_.o, _gsilib.o </snip> _gsilib.c and _gambcgsi.c both have ___LIBRARY defined. _gsi.c and _gsi_.c do not. So my questions are: is this a known problem with windows? Im I trying to use the correct files to build gsi? Compiler is metroworks code warrior, but I don't think it's fully a comiler specific issue. Regards Ivan

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[ANN] Gambit-C v4.5.1 released
by gambit＠iro.umontreal.ca 07 Aoû '09

07 Aoû '09

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Compiling GSI on windows with ___SHARED defined
by Ivan Kelly 07 Aoû '09

07 Aoû '09

Im compiling gambit on windows with ___SHARED defined, in a symbian OS emulator environment. I've managed to get it working without issue compiling to one big monolith, taking pointers from the openwatcom batch file (also compiled with gcce and running on phone). However, ___SHARED is proving to be a bit more difficult. The dll compiles with very little issue. ___LIBRARY and ___PRIMAL are defined for all *.c inputs to that, and it compiles without error apart from the unused variables, whose warnings i've hidden. gsi is proving trickier though. In getting a load of errors for ___gstate being defined in many places. Also, ___G__20__gsilib is twice defined. <snip> mwldsym2.exe: Multiply defined symbol: struct ___global_state_struct ___gstate (?___gstate@@3U___global_state_struct@@A) in mwldsym2.exe: files _gambcgsi.o, _gsilib.o mwldsym2.exe: Multiply defined symbol: struct ___glo_struct ___G__20___gsilib (?___G__20___gsilib@@3U___glo_struct@@A) in mwldsym2.exe: files _gambcgsi.o, _gsilib.o mwldsym2.exe: Multiply defined symbol: struct ___global_state_struct ___gstate (?___gstate@@3U___global_state_struct@@A) in mwldsym2.exe: files _gsi.o, _gsilib.o mwldsym2.exe: Multiply defined symbol: struct ___global_state_struct ___gstate (?___gstate@@3U___global_state_struct@@A) in mwldsym2.exe: files _gsi_.o, _gsilib.o </snip> _gsilib.c and _gambcgsi.c both have ___LIBRARY defined. _gsi.c and _gsi_.c do not. So my questions are: is this a known problem with windows? Im I trying to use the correct files to build gsi? Compiler is metroworks code warrior, but I don't think it's fully a comiler specific issue. Regards Ivan

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location in source code
by lowly coder 06 Aoû '09

06 Aoû '09

Is there a command, say "foo" that I can type at the command prompt, so it'll tell me what *.scm file (and line number) said function/macro comes from? Ideally something like: ,foo load or (foo 'load) and I get: lib/_eval.scm 3961 Thanks!

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importing in define
by lowly coder 06 Aoû '09

06 Aoû '09

foo.scm: (namespace ("foo#")) (##define define 2) [some code] (my-define ...) define ---- Is there something I can replace [some code] with, so that: 1) I'm still in namespace foo# 2) foo#my-define = ""#define 3) define still has value 2 on the last line [I'm doing some weird tricks where define does type checking on its args at run time.] Thanks!

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