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SQLite training in Houston TX on 2019-11-05 (details)
Part of the 2019 Tcl Conference

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Overview
Comment:Simplifications to the overflow-free multiplier. Also remove some commented-out code that was left in that subroutine by mistake on the previous check-in.
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SHA1: 55fc25fdab61e6094289e068c343e012fec10439
User & Date: drh 2011-03-05 21:41:34
Context
2011-03-06
21:28
Remove dead code identified by the clang static analyzer. check-in: 01a79d5a user: drh tags: trunk
2011-03-05
21:41
Simplifications to the overflow-free multiplier. Also remove some commented-out code that was left in that subroutine by mistake on the previous check-in. check-in: 55fc25fd user: drh tags: trunk
20:59
Fix all known instances of signed-integer overflow. Within SQL expressions, integer overflow now forces coercion to floating point. The shift operators work with any integer right-hand operand with negative values reversing the direction of the shift. check-in: abf21394 user: drh tags: trunk
Changes
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Changes to src/util.c.

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}
#define TWOPOWER32 (((i64)1)<<32)
#define TWOPOWER31 (((i64)1)<<31)
int sqlite3MulInt64(i64 *pA, i64 iB){
  i64 iA = *pA;
  i64 iA1, iA0, iB1, iB0, r;

//  if( iB==1 ){ return 0; }
//  if( iA==1 ){ *pA = iB; return 0; }
  iA1 = iA/TWOPOWER32;
  iA0 = iA % TWOPOWER32;
  iB1 = iB/TWOPOWER32;
  iB0 = iB % TWOPOWER32;
  if( iA1*iB1 != 0 ) return 1;
  r = iA1*iB0;
  if( sqlite3AddInt64(&r, iA0*iB1) ) return 1;
  testcase( r==(-TWOPOWER31)-1 );
  testcase( r==(-TWOPOWER31) );
  testcase( r==TWOPOWER31 );
  testcase( r==TWOPOWER31-1 );
  if( r<(-TWOPOWER31) || r>=TWOPOWER31 ) return 1;
  r *= TWOPOWER32;
  if( sqlite3AddInt64(&r, iA0*iB0) ) return 1;
  *pA = r;
  return 0;
}







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}
#define TWOPOWER32 (((i64)1)<<32)
#define TWOPOWER31 (((i64)1)<<31)
int sqlite3MulInt64(i64 *pA, i64 iB){
  i64 iA = *pA;
  i64 iA1, iA0, iB1, iB0, r;



  iA1 = iA/TWOPOWER32;
  iA0 = iA % TWOPOWER32;
  iB1 = iB/TWOPOWER32;
  iB0 = iB % TWOPOWER32;
  if( iA1*iB1 != 0 ) return 1;
  assert( iA1*iB0==0 || iA0*iB1==0 );
  r = iA1*iB0 + iA0*iB1;
  testcase( r==(-TWOPOWER31)-1 );
  testcase( r==(-TWOPOWER31) );
  testcase( r==TWOPOWER31 );
  testcase( r==TWOPOWER31-1 );
  if( r<(-TWOPOWER31) || r>=TWOPOWER31 ) return 1;
  r *= TWOPOWER32;
  if( sqlite3AddInt64(&r, iA0*iB0) ) return 1;
  *pA = r;
  return 0;
}