NAME

src/utils.c - Some utility functions

DESCRIPTION

Prototypes are in src/misc.h.

Opcode helper functions that don't really fit elsewhere.

Functions

INTVAL intval_mod

NOTE: This "corrected mod" algorithm is based on the C code on page 70 of [1]. Assuming correct behavior of the built-in mod operator (%) with positive arguments, this algorithm implements a mathematically convenient version of mod, defined thus:

    x mod y = x - y * floor(x / y)

For more information on this definition of mod, see section 3.4 of [2], pages 81-85.

References:

[1] Donald E. Knuth, *MMIXware: A RISC Computer for the Third Millennium* Springer, 1999.

[2] Ronald L. Graham, Donald E. Knuth and Oren Patashnik, *Concrete Mathematics*, Second Edition. Addison-Wesley, 1994.

FLOATVAL floatval_mod

Returns n2 mod n3.

Includes a workaround for buggy code generation in the lcc compiler.

Random Number Generator

Based on the rand48() family of functions.

static void next_rand

Returns the next random number in X.

static FLOATVAL _erand48

Returns a double in the interval [0.0, 1.0).

static FLOATVAL _drand48

Returns a double in the interval [0.0, 1.0).

static long _jrand48

Returns a long in the interval [-2^31, 2^31).

static long _nrand48

Returns a long in the interval [0, 2^31).

static long _lrand48

Returns a long in the interval [0, 2^31).

static long _mrand48

Returns a long in the interval [-2^31, 2^31).

static void _srand48

Sets the high order 32 bits to the argument seed. The low order 16 bits are set to the arbitrary value 0x330e.

FLOATVAL Parrot_float_rand

Returns a FLOATVAL in the interval [0.0, 1.0).

how_random is ignored.

INTVAL Parrot_uint_rand

Returns an INTVAL in the interval [0, 2^31).

how_random is ignored.

INTVAL Parrot_int_rand

Returns an INTVAL in the interval [-2^31, 2^31).

how_random is ignored.

INTVAL Parrot_range_rand

Returns an INTVAL in the range [from, to].

how_random is ignored.

void Parrot_srand

Seeds the random number generator with seed.

PMC *tm_to_array

Helper to convert a struct tm * to an Array

INTVAL Parrot_byte_index

Looks for the location of a substring within a longer string. Takes pointers to the strings and the offset within the string at which to start searching as arguments.

Returns an offset value if it is found, or -1 if no match.

INTVAL Parrot_byte_rindex

Substring search (like Parrot_byte_index), but works backwards, from the rightmost end of the string.

Returns offset value or -1 (if no match).

static void rec_climb_back_and_mark

Recursive function, used by Parrot_register_move to climb back the graph of register moves operations.

The node must have a predecessor: it is implicit because if a node has a node_index, it must have a predecessor because the node_index are the index of registers in dest_regs[] array, so by definition they have a corrsponding src_regs register.

Then it emits the move operation with its predecessor, or its backup if already used/visited.

Then continues the climbing if the predecessor was not modified, anf in that case marks it, and set node_index as its backup.

  node_index  ... the index of a destination (i.e. with a pred.) register
  c           ... the graph and all the needed params : the context

static void process_cycle_without_exit

Recursive function, used by Parrot_register_move to handle the case of cycles without exits, that are cycles of move ops between registers where each register has exactly one predecessor and one successor

For instance: 1-->2, 2-->3, 3-->1

  node_index  ... the index of a destination (i.e. with a pred.) register
  c           ... the graph and all the needed params : the context

void Parrot_register_move

Move n_regs from the given register list src_regs to dest_regs.

  n_regs    ... amount of registers to move
  dest_regs ... list of register numbers 0..255
  src_regs  ... list of register numbers 0..255
  temp_reg  ... a register number not in one of these lists
  mov       ... a register move function to be called to move one register
  mov_alt   ... a register move function to be called to move one register
                which triese fetching from an alternate src (or NULLfunc):

    (void)  (mov)(interp, dest, src, info);
    moved = (mov_alt)(interp, dest, src, info);

Some dest_regs might be the same as src_regs, which makes this a bit non-trivial, because if the destination is already clobbered, using it later as source doesn"t work. E.g.

  0 <- 1
  1 <- 0     # register 0 already clobbered

or

  2 <- 0
  0 <- 1
  3 <- 2      # register 2 already clobbered - reorder moves

To handle such cases, we do:

  a) rearrange the order of moves (not possible in the first case)
     and/or if that failed:
  b) if an alternate move function is available, it may fetch the
     source from a different (non-clobbered) location - call it.
     if the function returns 0 also use c)
  c) if no alternate move function is available, use the temp reg

The amount of register moves should of course be minimal.

TODO The current implementation will not work for following cases

Talked to Leo and he said those cases are not likely (Vishal Soni). 1. I0->I1 I1->I0 I0->I3 2. I1->I2 I3->I2

TODO: Add tests for the above conditions.

HISTORY

Initial version by leo 2003.09.09.