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Overview
Comment:Test versions of getVarint functions. The updates essentially utilize loop unrolling and some shifting/anding tricks to minimize the number of logical operations required. (CVS 5072)
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SHA1: 682dc24dbe82d0326377e27c5ff97db3499873b0
User & Date: shane 2008-05-01 02:47:04
Context
2008-05-01
17:03
Fix harmless compiler warnings. (CVS 5073) check-in: 227a6f67 user: drh tags: trunk
02:47
Test versions of getVarint functions. The updates essentially utilize loop unrolling and some shifting/anding tricks to minimize the number of logical operations required. (CVS 5072) check-in: 682dc24d user: shane tags: trunk
2008-04-30
16:38
Add comment to speculate when setting journal_mode=OFF on VACUUM does not help performance. No changes to code. (CVS 5071) check-in: 9c8b4bab user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/util.c.

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**
*************************************************************************
** Utility functions used throughout sqlite.
**
** This file contains functions for allocating memory, comparing
** strings, and stuff like that.
**
** $Id: util.c,v 1.224 2008/04/28 17:41:31 shane Exp $
*/
#include "sqliteInt.h"
#include <stdarg.h>
#include <ctype.h>


/*
................................................................................
}

/*
** Read a 64-bit variable-length integer from memory starting at p[0].
** Return the number of bytes read.  The value is stored in *v.
*/
int sqlite3GetVarint(const unsigned char *p, u64 *v){
  u32 x;
  u64 x64;

  int n;
  unsigned char c;
  if( ((c = p[0]) & 0x80)==0 ){

    *v = c;
    return 1;
  }






  x = c & 0x7f;
  if( ((c = p[1]) & 0x80)==0 ){


    *v = (x<<7) | c;
    return 2;
  }
  x = (x<<7) | (c&0x7f);
  if( ((c = p[2]) & 0x80)==0 ){











    *v = (x<<7) | c;
    return 3;
  }
  x = (x<<7) | (c&0x7f);
  if( ((c = p[3]) & 0x80)==0 ){














    *v = (x<<7) | c;
    return 4;
  }
  x64 = (x<<7) | (c&0x7f);







  n = 4;
  do{




















































































    c = p[n++];
    if( n==9 ){
      x64 = (x64<<8) | c;
      break;



    }
    x64 = (x64<<7) | (c&0x7f);
  }while( (c & 0x80)!=0 );
  *v = x64;


  return n;
}

/*
** Read a 32-bit variable-length integer from memory starting at p[0].
** Return the number of bytes read.  The value is stored in *v.
** A MACRO version, getVarint32, is provided which inlines the 
** single-byte case.  All code should use the MACRO version as 
** this function assumes the single-byte case has already been handled.
*/
int sqlite3GetVarint32(const unsigned char *p, u32 *v){
  u32 x;
  int n;
  unsigned char c;



#ifndef getVarint32
  if( ((signed char*)p)[0]>=0 ){


    *v = p[0];
    return 1;
  }
#endif






  x = p[0] & 0x7f;
  if( ((signed char*)p)[1]>=0 ){
    *v = (x<<7) | p[1];


    return 2;
  }
  x = (x<<7) | (p[1] & 0x7f);









  n = 2;
  do{
    x = (x<<7) | ((c = p[n++])&0x7f);
  }while( (c & 0x80)!=0 && n<9 );
  *v = x;
  return n;













































































}

/*
** Return the number of bytes that will be needed to store the given
** 64-bit integer.
*/
int sqlite3VarintLen(u64 v){







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**
*************************************************************************
** Utility functions used throughout sqlite.
**
** This file contains functions for allocating memory, comparing
** strings, and stuff like that.
**
** $Id: util.c,v 1.225 2008/05/01 02:47:04 shane Exp $
*/
#include "sqliteInt.h"
#include <stdarg.h>
#include <ctype.h>


/*
................................................................................
}

/*
** Read a 64-bit variable-length integer from memory starting at p[0].
** Return the number of bytes read.  The value is stored in *v.
*/
int sqlite3GetVarint(const unsigned char *p, u64 *v){
  u32 a,b,s;


  a = *p;
  // a: p0 (unmasked)
  if (!(a&0x80))
  {
    *v = a;
    return 1;
  }

  p++;
  b = *p;
  // b: p1 (unmasked)
  if (!(b&0x80))
  {
    a &= 0x7f;

    a = a<<7;
    a |= b;
    *v = a;
    return 2;
  }



  p++;
  a = a<<14;
  a |= *p;
  // a: p0<<14 | p2 (unmasked)
  if (!(a&0x80))
  {
    a &= (0x7f<<14)|(0x7f);
    b &= 0x7f;
    b = b<<7;
    a |= b;
    *v = a;
    return 3;
  }



  // CSE1 from below
  a &= (0x7f<<14)|(0x7f);
  p++;
  b = b<<14;
  b |= *p;
  // b: p1<<14 | p3 (unmasked)
  if (!(b&0x80))
  {
    b &= (0x7f<<14)|(0x7f);
    // moved CSE1 up
    // a &= (0x7f<<14)|(0x7f);
    a = a<<7;
    a |= b;
    *v = a;
    return 4;
  }


  // a: p0<<14 | p2 (masked)
  // b: p1<<14 | p3 (unmasked)
  // 1:save off p0<<21 | p1<<14 | p2<<7 | p3 (masked)
  // moved CSE1 up
  // a &= (0x7f<<14)|(0x7f);
  b &= (0x7f<<14)|(0x7f);
  s = a;

  // s: p0<<14 | p2 (masked)

  p++;
  a = a<<14;
  a |= *p;
  // a: p0<<28 | p2<<14 | p4 (unmasked)
  if (!(a&0x80))
  {
    // we can skip these cause they were (effectively) done above in calc'ing s
    // a &= (0x7f<<28)|(0x7f<<14)|(0x7f);
    // b &= (0x7f<<14)|(0x7f);
    b = b<<7;
    a |= b;
    s = s>>18;
    *v = ((u64)s)<<32 | a;
    return 5;
  }

  // 2:save off p0<<21 | p1<<14 | p2<<7 | p3 (masked)
  s = s<<7;
  s |= b;
  // s: p0<<21 | p1<<14 | p2<<7 | p3 (masked)

  p++;
  b = b<<14;
  b |= *p;
  // b: p1<<28 | p3<<14 | p5 (unmasked)
  if (!(b&0x80))
  {
    // we can skip this cause it was (effectively) done above in calc'ing s
    // b &= (0x7f<<28)|(0x7f<<14)|(0x7f);
    a &= (0x7f<<14)|(0x7f);
    a = a<<7;
    a |= b;
    s = s>>18;
    *v = ((u64)s)<<32 | a;
    return 6;
  }

  p++;
  a = a<<14;
  a |= *p;
  // a: p2<<28 | p4<<14 | p6 (unmasked)
  if (!(a&0x80))
  {
    a &= (0x7f<<28)|(0x7f<<14)|(0x7f);
    b &= (0x7f<<14)|(0x7f);
    b = b<<7;
    a |= b;
    s = s>>11;
    *v = ((u64)s)<<32 | a;
    return 7;
  }

  // CSE2 from below
  a &= (0x7f<<14)|(0x7f);
  p++;
  b = b<<14;
  b |= *p;
  // b: p3<<28 | p5<<14 | p7 (unmasked)
  if (!(b&0x80))
  {
    b &= (0x7f<<28)|(0x7f<<14)|(0x7f);
    // moved CSE2 up
    // a &= (0x7f<<14)|(0x7f);
    a = a<<7;
    a |= b;
    s = s>>4;
    *v = ((u64)s)<<32 | a;
    return 8;
  }

  p++;
  a = a<<15;
  a |= *p;
  // a: p4<<29 | p6<<15 | p8 (unmasked)

  // moved CSE2 up
  // a &= (0x7f<<29)|(0x7f<<15)|(0xff);
  b &= (0x7f<<14)|(0x7f);
  b = b<<8;
  a |= b;

  s = s<<4;
  b = p[-4];



  b &= 0x7f;
  b = b>>3;
  s |= b;




  *v = ((u64)s)<<32 | a;

  return 9;
}

/*
** Read a 32-bit variable-length integer from memory starting at p[0].
** Return the number of bytes read.  The value is stored in *v.
** A MACRO version, getVarint32, is provided which inlines the 
** single-byte case.  All code should use the MACRO version as 
** this function assumes the single-byte case has already been handled.
*/
int sqlite3GetVarint32(const unsigned char *p, u32 *v){
  u32 a,b;



  a = *p;
  // a: p0 (unmasked)
#ifndef getVarint32

  if (!(a&0x80))
  {
    *v = a;
    return 1;
  }
#endif

  p++;
  b = *p;
  // b: p1 (unmasked)
  if (!(b&0x80))
  {
    a &= 0x7f;


    a = a<<7;
    *v = a | b;
    return 2;
  }


  p++;
  a = a<<14;
  a |= *p;
  // a: p0<<14 | p2 (unmasked)
  if (!(a&0x80))
  {
    a &= (0x7f<<14)|(0x7f);
    b &= 0x7f;
    b = b<<7;



    *v = a | b;
    return 3;
  }

  p++;
  b = b<<14;
  b |= *p;
  // b: p1<<14 | p3 (unmasked)
  if (!(b&0x80))
  {
    b &= (0x7f<<14)|(0x7f);
    a &= (0x7f<<14)|(0x7f);
    a = a<<7;
    *v = a | b;
    return 4;
  }

  p++;
  a = a<<14;
  a |= *p;
  // a: p0<<28 | p2<<14 | p4 (unmasked)
  if (!(a&0x80))
  {
    a &= (0x7f<<28)|(0x7f<<14)|(0x7f);
    b &= (0x7f<<28)|(0x7f<<14)|(0x7f);
    b = b<<7;
    *v = a | b;
    return 5;
  }

  p++;
  b = b<<14;
  b |= *p;
  // b: p1<<28 | p3<<14 | p5 (unmasked)
  if (!(b&0x80))
  {
    b &= (0x7f<<28)|(0x7f<<14)|(0x7f);
    a &= (0x7f<<28)|(0x7f<<14)|(0x7f);
    a = a<<7;
    *v = a | b;
    return 6;
  }

  p++;
  a = a<<14;
  a |= *p;
  // a: p2<<28 | p4<<14 | p6 (unmasked)
  if (!(a&0x80))
  {
    a &= (0x7f<<28)|(0x7f<<14)|(0x7f);
    b &= (0x7f<<28)|(0x7f<<14)|(0x7f);
    b = b<<7;
    *v = a | b;
    return 7;
  }

  p++;
  b = b<<14;
  b |= *p;
  // b: p3<<28 | p5<<14 | p7 (unmasked)
  if (!(b&0x80))
  {
    b &= (0x7f<<28)|(0x7f<<14)|(0x7f);
    a &= (0x7f<<28)|(0x7f<<14)|(0x7f);
    a = a<<7;
    *v = a | b;
    return 8;
  }

  p++;
  a = a<<14;
  a |= *p;
  // a: p4<<28 | p6<<14 | p8 (unmasked)

  a &= (0x7f<<28)|(0x7f<<14)|(0x7f);
  b &= (0x7f<<28)|(0x7f<<14)|(0x7f);
  b = b<<7;
  *v = a | b;
  return 9;
}

/*
** Return the number of bytes that will be needed to store the given
** 64-bit integer.
*/
int sqlite3VarintLen(u64 v){