android / platform / bionic / e360a1c8a389772718814d291978390e0b662805 / . / libc / tzcode / difftime.c

/* | |

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

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

*/ | |

/*LINTLIBRARY*/ | |

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

/* Return -X as a double. Using this avoids casting to 'double'. */ | |

static double | |

dminus(double x) | |

{ | |

return -x; | |

} | |

double ATTRIBUTE_CONST | |

difftime(time_t time1, time_t time0) | |

{ | |

/* | |

** If double is large enough, simply convert and subtract | |

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

*/ | |

if (sizeof (time_t) < sizeof (double)) { | |

double t1 = time1, t0 = time0; | |

return t1 - t0; | |

} | |

/* | |

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

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

*/ | |

if (!TYPE_SIGNED(time_t)) | |

return time0 <= time1 ? time1 - time0 : dminus(time0 - time1); | |

/* Use uintmax_t if wide enough. */ | |

if (sizeof (time_t) <= sizeof (uintmax_t)) { | |

uintmax_t t1 = time1, t0 = time0; | |

return time0 <= time1 ? t1 - t0 : dminus(t0 - t1); | |

} | |

/* | |

** 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; | |

/* | |

** The values have opposite signs and uintmax_t is too narrow. | |

** This suffers from double rounding; attempt to lessen that | |

** by using long double temporaries. | |

*/ | |

{ | |

long double t1 = time1, t0 = time0; | |

return t1 - t0; | |

} | |

} |