Commit d3d86b17 authored by Nick Mathewson's avatar Nick Mathewson 🥔
Browse files

r12916@catbus: nickm | 2007-05-24 12:43:45 -0400 

 Add math functions to round values to the nearest power of 2.  Make mempools more careful about making sure that the size of their chunks is a little less than a power of 2, not a little more.


svn:r10304
parent d0a5c4f9

doc/TODO

+1 −0
Original line number Diff line number Diff line
@@ -83,6 +83,7 @@ Things we'd like to do in 0.2.0.x: 
        - Push/pull documents as appropriate.

        o Have clients know which authorities are v3 authorities, and what

          their keys are.

          - While we're at it, let v3 authorities have fqdns lines.

      - Start caching consensus documents once authorities make them

      - Start downloading and using consensus documents once caches serve them

    . 104: Long and Short Router Descriptors (by Jun 1)

src/common/compat.h

+2 −0
Original line number Diff line number Diff line
@@ -96,6 +96,7 @@ extern INLINE double U64_TO_DBL(uint64_t x) { 
#if defined(__GNUC__) && __GNUC__ >= 3

#define ATTR_NORETURN __attribute__((noreturn))

#define ATTR_PURE __attribute__((pure))

#define ATTR_CONST __attribute__((const))

#define ATTR_MALLOC __attribute__((malloc))

#define ATTR_NORETURN __attribute__((noreturn))

#define ATTR_NONNULL(x) __attribute__((nonnull x))
@@ -108,6 +109,7 @@ extern INLINE double U64_TO_DBL(uint64_t x) { 
#else

#define ATTR_NORETURN

#define ATTR_PURE

#define ATTR_CONST

#define ATTR_MALLOC

#define ATTR_NORETURN

#define ATTR_NONNULL(x)

src/common/mempool.c

+10 −4
Original line number Diff line number Diff line
@@ -361,18 +361,24 @@ mp_pool_new(size_t item_size, size_t chunk_capacity) 
  /* Now we figure out how many items fit in each chunk.  We need to fit at

   * least 2 items per chunk. No chunk can be more than MAX_CHUNK bytes long,

   * or less than MIN_CHUNK. */

  /* XXXX020 Try a bit harder here: we want to be a bit less than a power of

     2, not a bit over. */

  if (chunk_capacity > MAX_CHUNK)

    chunk_capacity = MAX_CHUNK;

  if (chunk_capacity < alloc_size * 2 + CHUNK_OVERHEAD)

    chunk_capacity = alloc_size * 2 + CHUNK_OVERHEAD;

  /* Try to be around a power of 2 in size, since that's what allocators like

   * handing out. 512K-1 byte is a lot better than 512K+1 byte. */

  chunk_capacity = (size_t) round_to_power_of_2(chunk_capacity);

  while (chunk_capacity < alloc_size * 2 + CHUNK_OVERHEAD)

    chunk_capacity *= 2;

  if (chunk_capacity < MIN_CHUNK)

    chunk_capacity = MIN_CHUNK;



  pool->new_chunk_capacity = (chunk_capacity-CHUNK_OVERHEAD) / alloc_size;

  pool->item_alloc_size = alloc_size;



  log_debug(LD_MM, "Capacity is %lu, item size is %lu, alloc size is %lu",

            (unsigned long)pool->new_chunk_capacity,

            (unsigned long)pool->item_alloc_size,

            (unsigned long)(pool->new_chunk_capacity*pool->item_alloc_size));



  return pool;

}

src/common/util.c

+48 −0
Original line number Diff line number Diff line
@@ -213,6 +213,54 @@ _tor_free(void *mem) 
  tor_free(mem);

}



/* =====

 * Math

 * ===== */



/** Returns floor(log2(u64)).  If u64 is 0, (incorrectly) returns 0. */

int

tor_log2(uint64_t u64)

{

  int r = 0;

  if (u64 >= (U64_LITERAL(1)<<32)) {

    u64 >>= 32;

    r = 32;

  }

  if (u64 >= (U64_LITERAL(1)<<16)) {

    u64 >>= 16;

    r += 16;

  }

  if (u64 >= (U64_LITERAL(1)<<8)) {

    u64 >>= 8;

    r += 8;

  }

  if (u64 >= (U64_LITERAL(1)<<4)) {

    u64 >>= 4;

    r += 4;

  }

  if (u64 >= (U64_LITERAL(1)<<2)) {

    u64 >>= 2;

    r += 2;

  }

  if (u64 >= (U64_LITERAL(1)<<1)) {

    u64 >>= 1;

    r += 1;

  }

  return r;

}



/** Return the power of 2 closest to <b>u64</b>. */

uint64_t

round_to_power_of_2(uint64_t u64)

{

  int lg2 = tor_log2(u64);

  uint64_t low = U64_LITERAL(1) << lg2, high = U64_LITERAL(1) << (lg2+1);

  if (high - u64 < u64 - low)

    return high;

  else

    return low;

}



/* =====

 * String manipulation

 * ===== */

src/common/util.h

+4 −0
Original line number Diff line number Diff line
@@ -142,6 +142,10 @@ extern int dmalloc_free(const char *file, const int line, void *pnt, 
/** Macro: true if two values have different boolean values. */

#define bool_neq(a,b) (!(a)!=!(b))



/* Math functions */

int tor_log2(uint64_t u64) ATTR_CONST;

uint64_t round_to_power_of_2(uint64_t u64);



/* String manipulation */



/** Allowable characters in a hexadecimal string. */