hex.cmp.init

This is where the compare “truth” tables are.
Its 8-bits are expected to be {src&lt;<4 | dst} at the jump to it (for the src,dst hexes of the cmp operation).
Its 8-bits are expected to be 0 after the jump to it.

Signature

def init @ switch, clean_table_entry, end < ..tables.ret > dst { ... }

Defined in hex/cond_jumps.fj — lines 139–160 (view on GitHub).

Complexity

  • Time: 6 (when jumping to dst, until finished)

  • Space: 514

See the complexity glossary for what @, w, dw, dbit, n mean.

Requires init

The following must be initialised before this macro is invoked:

  • hex.tables.init_shared (or hex.init)

Output labels

This macro exposes labels into the caller’s scope via >:

  • dst — This variable is an 8-bit variable (in a single op, [dbit,dbit+8)).

Source

Click to view the macro body

def init @ switch, clean_table_entry, end < ..tables.ret > dst {
    ;end
  dst: ;.switch

    pad 256
  switch:
    // The next line is the compare flipping-table.
    // The [src<<4 | dst] entry flips bits in hex.tables.ret:
    //   if dst  > src:     flips dbit+1
    //   if dst == src:     flips dbit+0
    //   if dst  < src:     no flips
    // Upon entering here, .dst was xored with the correct table-entry, and was jumped into.
    rep(256, d) stl.fj  ((d&0xf) > (d>>4)) \
                         ? ..tables.ret+dbit+1 \
                         : (((d&0xf) == (d>>4)) ? ..tables.ret+dbit : 0),\
                        clean_table_entry+d*dw

  clean_table_entry:
    // xors back the table-entry from .dst
    ..tables.clean_table_entry__table .dst
  end:
}

Depends on

Used by

Example uses

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