Merge pull request #76 from synopse/main

abouchez/mormot: reduce memory consumption

Author: gcarreno

entries/abouchez/README.md

@@ -62,6 +62,7 @@ Here are the main ideas behind this implementation proposal:
 - The station names are stored as UTF-8 pointers to the memmap location where they appear first, in `StationName[]`, to be emitted eventually for the final output, not during temperature parsing;
 - No memory allocation (e.g. no transient `string` or `TBytes`) nor any syscall is done during the parsing process to reduce contention and ensure the process is only CPU-bound and RAM-bound (we checked this with `strace` on Linux);
 - Pascal code was tuned to generate the best possible asm output on FPC x86_64 (which is our target) - perhaps making it less readable, because we used pointer arithmetics when it matters (I like to think as such low-level pascal code as [portable assembly](https://sqlite.org/whyc.html#performance) similar to "unsafe" code in managed languages);
+- We even tried an optimized SSE2 asm sub-function for searching the name `';'` delimiter - which is a O(n) part of the process, and in practice... it was slower than a slightly unrolled pure pascal inlined loop;
 - It can optionally output timing statistics and resultset hash value on the console to debug and refine settings (with the `-v` command line switch);
 - It can optionally set each thread affinity to a single core (with the `-a` command line switch).
 

entries/abouchez/src/brcmormot.lpr

@@ -172,7 +172,7 @@ function NameLen(p: PUtf8Char): PtrInt; inline;
         exit(result + 1)
     else
       exit;
-  // this small (unrolled) inlined loop is as fast as the SSE2 :)
+  // this small (unrolled) inlined loop is faster than a SSE2 function :)
 end;
 {$endif FPC_CPUX64}
 
@@ -216,7 +216,7 @@ procedure TBrcThread.Execute;
       inc(s^.Count);
       m := s^.Min;
       if v < m then
-        m := v; // branchless cmovl
+        m := v; // branchless cmovg/cmovl
       s^.Min := m;
       m := s^.Max;
       if v > m then
@@ -243,7 +243,6 @@ constructor TBrcMain.Create(const fn: TFileName; threads, chunkmb, max: integer;
     raise ESynException.CreateUtf8('Impossible to find %', [fn]);
   fMax := max;
   fChunkSize := chunkmb shl 20;
-  fList.Init(fMax);
   fCurrentChunk := pointer(fMem.Buffer);
   fCurrentRemain := fMem.Size;
   core := 0;