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/ Developer CD Series 1996 May: Tool Chest / Developer CD Series May 1996 (Tool Chest) (Apple Computer) (1996).iso / Sample Code / SCSI Samples 1.0 / SCSI Async Sample 06⁄15 ƒ / Src / MicrosecondDelta.c < prev    next >
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C/C++ Source or Header  |  1994-06-16  |  1.0 KB  |  45 lines  |  [TEXT/KAHL]
  1. /*                                    MicrosecondDelta.c                                */
  2. /*
  3.  * MicrosecondDelta.c
  4.  * Copyright © 1994 Apple Computer Inc. All rights reserved.
  5.  */
  6. #include "MicrosecondTrap.h"
  7.  
  8. /*
  9.  * Convert an epoch to microseconds (use floating-point operations).
  10.  * Note that 4294967296.0 is 2^32, which is represented accurately
  11.  * in double-precision floating point. Note that this can loose
  12.  * low-order bits.
  13.  */
  14. #define kTwoPower32 (4294967296.0)
  15.  
  16. double
  17. MicrosecondToDouble(
  18.         register const UnsignedWide    *epochPtr
  19.     )
  20. {
  21.         register double            result;
  22.         
  23.         result = (((double) epochPtr->hi) * kTwoPower32) + epochPtr->lo;
  24.         return (result);
  25. }
  26.  
  27. /*
  28.  * Return the difference between two Microsecond Trap values.
  29.  * Integer subtraction is used to preserve accuracy.
  30.  */
  31. void
  32. MicrosecondDelta(
  33.         register const UnsignedWide    *startPtr,
  34.         register const UnsignedWide    *endPtr,
  35.         register UnsignedWide        *result
  36.     )
  37. {
  38.         if (endPtr->lo >= startPtr->lo)
  39.             result->hi = endPtr->hi - startPtr->hi;
  40.         else {
  41.             result->hi = (endPtr->hi - 1) - startPtr->hi;
  42.         }
  43.         result->lo = endPtr->lo - startPtr->lo;
  44. }
  45.