D. J. Bernstein

The taia library interface

Times with 1-attosecond precision

     #include <taia.h>

     struct taia t;
A struct taia value is a number between 0 inclusive and 2^64 exclusive. The number is a multiple of 10^-18. The format of struct taia is designed to speed up common operations; applications should not look inside struct taia.

A struct taia variable is commonly used to store a TAI64NA label. Each TAI64NA label refers to one attosecond of real time. The number in the struct taia is the second count, plus 10^-9 times the nanosecond count, plus 10^-18 times the attosecond count.

A struct taia variable may also be used to store the numerical difference between two TAI64NA labels.

Current time

     #include <taia.h>

     struct taia t;

taia_now puts the current time into t. More precisely: taia_now puts into t its best guess as to the TAI64NA label for the 1-attosecond interval that contains the current time.

The current implementation of taia_now assumes that the struct timeval returned by the UNIX gettimeofday function represents the number of TAI seconds since 1970-01-01 00:00:10 TAI. This matches the convention used by the Olson tz library in ``right'' mode. Beware that many clocks are not set accurately, and even the best scientific clocks are nowhere near 1-attosecond accuracy; however, an inaccurate clock may still produce reasonably accurate time differences.

Binary input and output

     #include <taia.h>

     struct taia t;
     char buf[TAIA_PACK];

taia_pack converts a TAI64NA label from internal format in t to external TAI64NA format in buf.

taia_pack converts a TAI64NA label from external TAI64NA format in buf to internal format in t.

TAIA_PACK is 16.

ASCII output

     #include <taia.h>

     struct taia t;
     char *s;
     unsigned int len;

     len = taia_fmtfrac(s,&t);
taia_fmtfrac prints the 18-digit fraction part of t in decimal, without a decimal point but with leading zeros, into the character buffer s, without a terminating \0. It returns 18, the number of characters written. s may be zero; then taia_fmtfrac returns 18 without printing anything.

The macro TAIA_FMTFRAC is defined as 19; this is enough space for the output of taia_fmtfrac and a terminating \0.


     #include <taia.h>

     struct taia t;
     struct taia a;
     struct taia b;
     struct tai sec;
     double d;
     int i;

     d = taia_approx(&t);
     d = taia_frac(&t);

     i = taia_less(&a,&b);
taia_approx returns a double-precision approximation to t. The result of taia_approx is always nonnegative.

taia_tai places into sec the integer part of t. sec is a struct tai variable. If t contains a TAI64NA label then sec will contain the corresponding TAI64 label.

taia_frac returns a double-precision approximation to the fraction part of t. The result of taia_frac is always nonnegative.

taia_less returns 1 if a is less than b, 0 otherwise.

taia_add adds a to b modulo 2^64 and puts the result into t. The inputs and output may overlap.

taia_sub subtracts b from a modulo 2^64 and puts the result into t. The inputs and output may overlap.

taia_half divides a by 2, rounding down to a multiple of 10^-18, and puts the result into t. The input and output may overlap.