text: #include "flecs_private.h"
  
  /** Convert time to double */
  double ecs_time_to_double(
      ecs_time_t t)
  {
      double result;
      result = t.sec;
      return result + (double)t.nanosec / (double)1000000000;;
  }
  
  ecs_time_t ecs_time_sub(
      ecs_time_t t1,
      ecs_time_t t2)
  {
      ecs_time_t result;
  
      if (t1.nanosec >= t2.nanosec) {
          result.nanosec = t1.nanosec - t2.nanosec;
          result.sec = t1.sec - t2.sec;
      } else {
          result.nanosec = t1.nanosec - t2.nanosec + 1000000000;
          result.sec = t1.sec - t2.sec - 1;
      }
  
      return result;
  }
  
  void ecs_sleepf(
      double t)
  {
      if (t > 0) {
          int sec = (int)t;
          int nsec = (((int)t - sec) * 1000000000);
          ecs_os_sleep(sec, nsec);
      }
  }
  
  double ecs_time_measure(
      ecs_time_t *start)
  {
      ecs_time_t stop, temp;
      ecs_os_get_time(&stop);
      temp = stop;
      stop = ecs_time_sub(stop, *start);
      *start = temp;
      return ecs_time_to_double(stop);
  }
  
  /*
      This code was taken from sokol_time.h 
      
      zlib/libpng license
      Copyright (c) 2018 Andre Weissflog
      This software is provided 'as-is', without any express or implied warranty.
      In no event will the authors be held liable for any damages arising from the
      use of this software.
      Permission is granted to anyone to use this software for any purpose,
      including commercial applications, and to alter it and redistribute it
      freely, subject to the following restrictions:
          1. The origin of this software must not be misrepresented; you must not
          claim that you wrote the original software. If you use this software in a
          product, an acknowledgment in the product documentation would be
          appreciated but is not required.
          2. Altered source versions must be plainly marked as such, and must not
          be misrepresented as being the original software.
          3. This notice may not be removed or altered from any source
          distribution.
  */
  
  #include "flecs_private.h"
  
  static int ecs_os_time_initialized;
  
  #if defined(_WIN32)
  #ifndef WIN32_LEAN_AND_MEAN
  #define WIN32_LEAN_AND_MEAN
  #endif
  #include <windows.h>
  static double _ecs_os_time_win_freq;
  static LARGE_INTEGER _ecs_os_time_win_start;
  #elif defined(__APPLE__) && defined(__MACH__)
  #include <mach/mach_time.h>
  static mach_timebase_info_data_t _ecs_os_time_osx_timebase;
  static uint64_t _ecs_os_time_osx_start;
  #else /* anything else, this will need more care for non-Linux platforms */
  #include <time.h>
  static uint64_t _ecs_os_time_posix_start;
  #endif
  
  /* prevent 64-bit overflow when computing relative timestamp
      see https://gist.github.com/jspohr/3dc4f00033d79ec5bdaf67bc46c813e3
  */
  #if defined(_WIN32) || (defined(__APPLE__) && defined(__MACH__))
  int64_t int64_muldiv(int64_t value, int64_t numer, int64_t denom) {
      int64_t q = value / denom;
      int64_t r = value % denom;
      return q * numer + r * numer / denom;
  }
  #endif
  
  void ecs_os_time_setup(void) {
      if ( ecs_os_time_initialized) {
          return;
      }
      
      ecs_os_time_initialized = 1;
      #if defined(_WIN32)
          LARGE_INTEGER freq;
          QueryPerformanceFrequency(&freq);
          QueryPerformanceCounter(&_ecs_os_time_win_start);
          _ecs_os_time_win_freq = (double)freq.QuadPart / 1000000000.0;
      #elif defined(__APPLE__) && defined(__MACH__)
          mach_timebase_info(&_ecs_os_time_osx_timebase);
          _ecs_os_time_osx_start = mach_absolute_time();
      #else
          struct timespec ts;
          clock_gettime(CLOCK_MONOTONIC, &ts);
          _ecs_os_time_posix_start = (uint64_t)ts.tv_sec*1000000000 + (uint64_t)ts.tv_nsec; 
      #endif
  }
  
  uint64_t ecs_os_time_now(void) {
      ecs_assert(ecs_os_time_initialized != 0, ECS_INTERNAL_ERROR, NULL);
  
      uint64_t now;
  
      #if defined(_WIN32)
          LARGE_INTEGER qpc_t;
          QueryPerformanceCounter(&qpc_t);
          now = (uint64_t)(qpc_t.QuadPart / _ecs_os_time_win_freq);
      #elif defined(__APPLE__) && defined(__MACH__)
          now = mach_absolute_time();
      #else
          struct timespec ts;
          clock_gettime(CLOCK_MONOTONIC, &ts);
          now = ((uint64_t)ts.tv_sec * 1000000000 + (uint64_t)ts.tv_nsec);
      #endif
  
      return now;
  }
  
  void ecs_os_time_sleep(
      unsigned int sec, 
      unsigned int nanosec) 
  {
  #ifndef _WIN32
      struct timespec sleepTime;
  
      sleepTime.tv_sec = sec;
      sleepTime.tv_nsec = nanosec;
      if (nanosleep(&sleepTime, NULL)) {
          ecs_os_err("nanosleep failed");
      }
  #else
  	Sleep(sec * 1000 + nanosec / 1000000);
  #endif
  }
  
  /*
   * http://burtleburtle.net/bob/c/lookup3.c
  -------------------------------------------------------------------------------
  lookup3.c, by Bob Jenkins, May 2006, Public Domain.
  
  These are functions for producing 32-bit hashes for hash table lookup.
  hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
  are externally useful functions.  Routines to test the hash are included
  if SELF_TEST is defined.  You can use this free for any purpose.  It's in
  the public domain.  It has no warranty.
  
  You probably want to use hashlittle().  hashlittle() and hashbig()
  hash byte arrays.  hashlittle() is is faster than hashbig() on
  little-endian machines.  Intel and AMD are little-endian machines.
  On second thought, you probably want hashlittle2(), which is identical to
  hashlittle() except it returns two 32-bit hashes for the price of one.
  You could implement hashbig2() if you wanted but I haven't bothered here.
  
  If you want to find a hash of, say, exactly 7 integers, do
    a = i1;  b = i2;  c = i3;
    mix(a,b,c);
    a += i4; b += i5; c += i6;
    mix(a,b,c);
    a += i7;
    final(a,b,c);
  then use c as the hash value.  If you have a variable length array of
  4-byte integers to hash, use hashword().  If you have a byte array (like
  a character string), use hashlittle().  If you have several byte arrays, or
  a mix of things, see the comments above hashlittle().
  
  Why is this so big?  I read 12 bytes at a time into 3 4-byte integers,
  then mix those integers.  This is fast (you can do a lot more thorough
  mixing with 12*3 instructions on 3 integers than you can with 3 instructions
  on 1 byte), but shoehorning those bytes into integers efficiently is messy.
  -------------------------------------------------------------------------------
  */
  
  #include "flecs_private.h"
  
  /*
   * My best guess at if you are big-endian or little-endian.  This may
   * need adjustment.
   */
  #if (defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && \
       __BYTE_ORDER == __LITTLE_ENDIAN) || \
      (defined(i386) || defined(__i386__) || defined(__i486__) || \
       defined(__i586__) || defined(__i686__) || defined(vax) || defined(MIPSEL))
  # define HASH_LITTLE_ENDIAN 1
  # define HASH_BIG_ENDIAN 0
  #elif (defined(__BYTE_ORDER) && defined(__BIG_ENDIAN) && \
         __BYTE_ORDER == __BIG_ENDIAN) || \
        (defined(sparc) || defined(POWERPC) || defined(mc68000) || defined(sel))
  # define HASH_LITTLE_ENDIAN 0
  # define HASH_BIG_ENDIAN 1
  #else
  # define HASH_LITTLE_ENDIAN 0
  # define HASH_BIG_ENDIAN 0
  #endif
  
  #define hashsize(n) ((uint32_t)1<<(n))
  #define hashmask(n) (hashsize(n)-1)
  #define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
  
  /*
  -------------------------------------------------------------------------------
  mix -- mix 3 32-bit values reversibly.
  
  This is reversible, so any information in (a,b,c) before mix() is
  still in (a,b,c) after mix().
  
  If four pairs of (a,b,c) inputs are run through mix(), or through
  mix() in reverse, there are at least 32 bits of the output that
  are sometimes the same for one pair and different for another pair.
  This was tested for:
  * pairs that differed by one bit, by two bits, in any combination
    of top bits of (a,b,c), or in any combination of bottom bits of
    (a,b,c).
  * "differ" is defined as +, -, ^, or ~^.  For + and -, I transformed
    the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
    is commonly produced by subtraction) look like a single 1-bit
    difference.
  * the base values were pseudorandom, all zero but one bit set, or
    all zero plus a counter that starts at zero.
  
  Some k values for my "a-=c; a^=rot(c,k); c+=b;" arrangement that
  satisfy this are
      4  6  8 16 19  4
      9 15  3 18 27 15
     14  9  3  7 17  3
  Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
  for "differ" defined as + with a one-bit base and a two-bit delta.  I
  used http://burtleburtle.net/bob/hash/avalanche.html to choose
  the operations, constants, and arrangements of the variables.
  
  This does not achieve avalanche.  There are input bits of (a,b,c)
  that fail to affect some output bits of (a,b,c), especially of a.  The
  most thoroughly mixed value is c, but it doesn't really even achieve
  avalanche in c.
  
  This allows some parallelism.  Read-after-writes are good at doubling
  the number of bits affected, so the goal of mixing pulls in the opposite
  direction as the goal of parallelism.  I did what I could.  Rotates
  seem to cost as much as shifts on every machine I could lay my hands
  on, and rotates are much kinder to the top and bottom bits, so I used
  rotates.
  -------------------------------------------------------------------------------
  */
  #define mix(a,b,c) \
  { \
    a -= c;  a ^= rot(c, 4);  c += b; \
    b -= a;  b ^= rot(a, 6);  a += c; \
    c -= b;  c ^= rot(b, 8);  b += a; \
    a -= c;  a ^= rot(c,16);  c += b; \
    b -= a;  b ^= rot(a,19);  a += c; \
    c -= b;  c ^= rot(b, 4);  b += a; \
  }
  
  /*
  -------------------------------------------------------------------------------
  final -- final mixing of 3 32-bit values (a,b,c) into c
  
  Pairs of (a,b,c) values differing in only a few bits will usually
  produce values of c that look totally different.  This was tested for
  * pairs that differed by one bit, by two bits, in any combination
    of top bits of (a,b,c), or in any combination of bottom bits of
    (a,b,c).
  * "differ" is defined as +, -, ^, or ~^.  For + and -, I transformed
    the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
    is commonly produced by subtraction) look like a single 1-bit
    difference.
  * the base values were pseudorandom, all zero but one bit set, or
    all zero plus a counter that starts at zero.
  
  These constants passed:
   14 11 25 16 4 14 24
   12 14 25 16 4 14 24
  and these came close:
    4  8 15 26 3 22 24
   10  8 15 26 3 22 24
   11  8 15 26 3 22 24
  -------------------------------------------------------------------------------
  */
  #define final(a,b,c) \
  { \
    c ^= b; c -= rot(b,14); \
    a ^= c; a -= rot(c,11); \
    b ^= a; b -= rot(a,25); \
    c ^= b; c -= rot(b,16); \
    a ^= c; a -= rot(c,4);  \
    b ^= a; b -= rot(a,14); \
    c ^= b; c -= rot(b,24); \
  }
  
  /*
  -------------------------------------------------------------------------------
  hashlittle() -- hash a variable-length key into a 32-bit value
    k       : the key (the unaligned variable-length array of bytes)
    length  : the length of the key, counting by bytes
    initval : can be any 4-byte value
  Returns a 32-bit value.  Every bit of the key affects every bit of
  the return value.  Two keys differing by one or two bits will have
  totally different hash values.
  
  The best hash table sizes are powers of 2.  There is no need to do
  mod a prime (mod is sooo slow!).  If you need less than 32 bits,
  use a bitmask.  For example, if you need only 10 bits, do
    h = (h & hashmask(10));
  In which case, the hash table should have hashsize(10) elements.
  
  If you are hashing n strings (uint8_t **)k, do it like this:
    for (i=0, h=0; i<n; ++i) h = hashlittle( k[i], len[i], h);
  
  By Bob Jenkins, 2006.  bob_jenkins@burtleburtle.net.  You may use this
  code any way you wish, private, educational, or commercial.  It's free.
  
  Use for hash table lookup, or anything where one collision in 2^^32 is
  acceptable.  Do NOT use for cryptographic purposes.
  -------------------------------------------------------------------------------
  */
  
  uint32_t hashlittle( const void *key, size_t length, uint32_t initval)
  {
    uint32_t a,b,c;                                          /* internal state */
    union { const void *ptr; size_t i; } u;     /* needed for Mac Powerbook G4 */
  
    /* Set up the internal state */
    a = b = c = 0xdeadbeef + ((uint32_t)length) + initval;
  
    u.ptr = key;
    if (HASH_LITTLE_ENDIAN && ((u.i & 0x3) == 0)) {
      const uint32_t *k = (const uint32_t *)key;         /* read 32-bit chunks */
  
      /*------ all but last block: aligned reads and affect 32 bits of (a,b,c) */
      while (length > 12)
      {
        a += k[0];
        b += k[1];
        c += k[2];
        mix(a,b,c);
        length -= 12;
        k += 3;
      }
  
      /*----------------------------- handle the last (probably partial) block */
      /*
       * "k[2]&0xffffff" actually reads beyond the end of the string, but
       * then masks off the part it's not allowed to read.  Because the
       * string is aligned, the masked-off tail is in the same word as the
       * rest of the string.  Every machine with memory protection I've seen
       * does it on word boundaries, so is OK with this.  But VALGRIND will
       * still catch it and complain.  The masking trick does make the hash
       * noticably faster for short strings (like English words).
       */
  #ifndef VALGRIND
  
      switch(length)
      {
      case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
      case 11: c+=k[2]&0xffffff; b+=k[1]; a+=k[0]; break;
      case 10: c+=k[2]&0xffff; b+=k[1]; a+=k[0]; break;
      case 9 : c+=k[2]&0xff; b+=k[1]; a+=k[0]; break;
      case 8 : b+=k[1]; a+=k[0]; break;
      case 7 : b+=k[1]&0xffffff; a+=k[0]; break;
      case 6 : b+=k[1]&0xffff; a+=k[0]; break;
      case 5 : b+=k[1]&0xff; a+=k[0]; break;
      case 4 : a+=k[0]; break;
      case 3 : a+=k[0]&0xffffff; break;
      case 2 : a+=k[0]&0xffff; break;
      case 1 : a+=k[0]&0xff; break;
      case 0 : return c;              /* zero length strings require no mixing */
      }
  
  #else /* make valgrind happy */
      const uint8_t  *k8;
  
      k8 = (const uint8_t *)k;
      switch(length)
      {
      case 12: c+=k[2]; b+=k[1]; a+=k[0]; break;
      case 11: c+=((uint32_t)k8[10])<<16;  /* fall through */
      case 10: c+=((uint32_t)k8[9])<<8;    /* fall through */
      case 9 : c+=k8[8];                   /* fall through */
      case 8 : b+=k[1]; a+=k[0]; break;
      case 7 : b+=((uint32_t)k8[6])<<16;   /* fall through */
      case 6 : b+=((uint32_t)k8[5])<<8;    /* fall through */
      case 5 : b+=k8[4];                   /* fall through */
      case 4 : a+=k[0]; break;
      case 3 : a+=((uint32_t)k8[2])<<16;   /* fall through */
      case 2 : a+=((uint32_t)k8[1])<<8;    /* fall through */
      case 1 : a+=k8[0]; break;
      case 0 : return c;
      }
  
  #endif /* !valgrind */
  
    } else if (HASH_LITTLE_ENDIAN && ((u.i & 0x1) == 0)) {
      const uint16_t *k = (const uint16_t *)key;         /* read 16-bit chunks */
      const uint8_t  *k8;
  
      /*--------------- all but last block: aligned reads and different mixing */
      while (length > 12)
      {
        a += k[0] + (((uint32_t)k[1])<<16);
        b += k[2] + (((uint32_t)k[3])<<16);
        c += k[4] + (((uint32_t)k[5])<<16);
        mix(a,b,c);
        length -= 12;
        k += 6;
      }
  
      /*----------------------------- handle the last (probably partial) block */
      k8 = (const uint8_t *)k;
      switch(length)
      {
      case 12: c+=k[4]+(((uint32_t)k[5])<<16);
               b+=k[2]+(((uint32_t)k[3])<<16);
               a+=k[0]+(((uint32_t)k[1])<<16);
               break;
      case 11: c+=((uint32_t)k8[10])<<16;     /* fall through */
      case 10: c+=k[4];
               b+=k[2]+(((uint32_t)k[3])<<16);
               a+=k[0]+(((uint32_t)k[1])<<16);
               break;
      case 9 : c+=k8[8];                      /* fall through */
      case 8 : b+=k[2]+(((uint32_t)k[3])<<16);
               a+=k[0]+(((uint32_t)k[1])<<16);
               break;
      case 7 : b+=((uint32_t)k8[6])<<16;      /* fall through */
      case 6 : b+=k[2];
               a+=k[0]+(((uint32_t)k[1])<<16);
               break;
      case 5 : b+=k8[4];                      /* fall through */
      case 4 : a+=k[0]+(((uint32_t)k[1])<<16);
               break;
      case 3 : a+=((uint32_t)k8[2])<<16;      /* fall through */
      case 2 : a+=k[0];
               break;
      case 1 : a+=k8[0];
               break;
      case 0 : return c;                     /* zero length requires no mixing */
      }
  
    } else {                        /* need to read the key one byte at a time */
      const uint8_t *k = (const uint8_t *)key;
  
      /*--------------- all but the last block: affect some 32 bits of (a,b,c) */
      while (length > 12)
      {
        a += k[0];
        a += ((uint32_t)k[1])<<8;
        a += ((uint32_t)k[2])<<16;
        a += ((uint32_t)k[3])<<24;
        b += k[4];
        b += ((uint32_t)k[5])<<8;
        b += ((uint32_t)k[6])<<16;
        b += ((uint32_t)k[7])<<24;
        c += k[8];
        c += ((uint32_t)k[9])<<8;
        c += ((uint32_t)k[10])<<16;
        c += ((uint32_t)k[11])<<24;
        mix(a,b,c);
        length -= 12;
        k += 12;
      }
  
      /*-------------------------------- last block: affect all 32 bits of (c) */
      switch(length)                   /* all the case statements fall through */
      {
      case 12: c+=((uint32_t)k[11])<<24;
      case 11: c+=((uint32_t)k[10])<<16;
      case 10: c+=((uint32_t)k[9])<<8;
      case 9 : c+=k[8];
      case 8 : b+=((uint32_t)k[7])<<24;
      case 7 : b+=((uint32_t)k[6])<<16;
      case 6 : b+=((uint32_t)k[5])<<8;
      case 5 : b+=k[4];
      case 4 : a+=((uint32_t)k[3])<<24;
      case 3 : a+=((uint32_t)k[2])<<16;
      case 2 : a+=((uint32_t)k[1])<<8;
      case 1 : a+=k[0];
               break;
      case 0 : return c;
      }
    }
  
    final(a,b,c);
    return c;
  }
  
  void ecs_hash(
      const void *key,
      size_t length,
      uint32_t *result)
  {
      *result = hashlittle(
          key,
          length,
          *(uint32_t*)result);
  }
  