SQLite

#
#       case OP_aaaa:      /* same as TK_bbbbb */
#
# The TK_ comment is optional.  If it is present, then the value assigned to
# the OP_ is the same as the TK_ value.  If missing, the OP_ value is assigned
# a small integer that is different from every other OP_ value.
#
# We go to the trouble of making some OP_ values the same as TK_ values
# as an optimization.  During parsing, things like expression operators
# are coded with TK_ values such as TK_ADD, TK_DIVIDE, and so forth.  Later
# during code generation, we need to generate corresponding opcodes like
# OP_Add and OP_Divide.  By making TK_ADD==OP_Add and TK_DIVIDE==OP_Divide,
# code to translate from one to the other is avoided.  This makes the
# code generator run (infinitesimally) faster and more importantly it makes
# the library footprint smaller.
#
# This script also scans for lines of the form:
#
#       case OP_aaaa:       /* no-push */
#
# When the no-push comment is found on an opcode, it means that that
# opcode does not leave a result on the stack.  By identifying which
# opcodes leave results on the stack it is possible to determine a
# much smaller upper bound on the size of the stack.  This allows
# a smaller stack to be allocated, which is important to embedded
# systems with limited memory space.  This script generates a series
# of "NOPUSH_MASK" defines that contain bitmaps of opcodes that leave
# results on the stack.  The NOPUSH_MASK defines are used in vdbeaux.c
# to help determine the maximum stack size.

      n = op[name]
      j = n%16
      i = ((n - j)/16)
      nopush[i] = nopush[i] + (2^j)
    }
  }
  printf "\n"
  print "/* Opcodes that are guaranteed to never push a value onto the stack"
  print "** contain a 1 their corresponding position of the following mask"
  print "** set.  See the opcodeNoPush() function in vdbeaux.c  */"
  for(i=0; i<10; i++){
    printf "#define NOPUSH_MASK_%d 0x%04x\n", i, nopush[i]
  }
}