android / platform / bionic / 0d787c1fa18c6a1f29ef9840e28a68cf077be1de / . / libc / tzcode / difftime.c

/* | |

** This file is in the public domain, so clarified as of | |

** 1996-06-05 by Arthur David Olson. | |

*/ | |

#ifndef lint | |

#ifndef NOID | |

static char elsieid[] = "@(#)difftime.c 8.1"; | |

#endif /* !defined NOID */ | |

#endif /* !defined lint */ | |

/*LINTLIBRARY*/ | |

#include "private.h" /* for time_t, TYPE_INTEGRAL, and TYPE_SIGNED */ | |

double | |

difftime(time1, time0) | |

const time_t time1; | |

const time_t time0; | |

{ | |

/* | |

** If (sizeof (double) > sizeof (time_t)) simply convert and subtract | |

** (assuming that the larger type has more precision). | |

** This is the common real-world case circa 2004. | |

*/ | |

if (sizeof (double) > sizeof (time_t)) | |

return (double) time1 - (double) time0; | |

if (!TYPE_INTEGRAL(time_t)) { | |

/* | |

** time_t is floating. | |

*/ | |

return time1 - time0; | |

} | |

if (!TYPE_SIGNED(time_t)) { | |

/* | |

** time_t is integral and unsigned. | |

** The difference of two unsigned values can't overflow | |

** if the minuend is greater than or equal to the subtrahend. | |

*/ | |

if (time1 >= time0) | |

return time1 - time0; | |

else return -((double) (time0 - time1)); | |

} | |

/* | |

** time_t is integral and signed. | |

** Handle cases where both time1 and time0 have the same sign | |

** (meaning that their difference cannot overflow). | |

*/ | |

if ((time1 < 0) == (time0 < 0)) | |

return time1 - time0; | |

/* | |

** time1 and time0 have opposite signs. | |

** Punt if unsigned long is too narrow. | |

*/ | |

if (sizeof (unsigned long) < sizeof (time_t)) | |

return (double) time1 - (double) time0; | |

/* | |

** Stay calm...decent optimizers will eliminate the complexity below. | |

*/ | |

if (time1 >= 0 /* && time0 < 0 */) | |

return (unsigned long) time1 + | |

(unsigned long) (-(time0 + 1)) + 1; | |

return -(double) ((unsigned long) time0 + | |

(unsigned long) (-(time1 + 1)) + 1); | |

} |