asin function

Synopsis

$asin(number)

Technical

asin() calls the C library's asin() function to return the principal arc sine of number. For a number between -1 and 1 inclusive, the result is between -pi/2 and pi/2 radians. It does not return degrees. sin() performs the corresponding sine operation.

The normal rules about number arguments apply. The first argument word is converted with atof(), accepting decimal fractions and scientific notation; additional words are ignored. Missing input returns the empty string. Nonnumeric input converts to zero, and a numeric prefix can be accepted even when followed by nonnumeric text.

Returns and restrictions

The calculation uses a C double, and results are formatted with %.50g. The floating_point_math and floating_point_precision settings do not change this function's calculation or formatting. Additional displayed rounding digits do not imply 50 digits of accuracy.

Arguments outside [-1, 1] cause a library domain error. EPIC returns DOM when the library reports that error through errno; if the platform reports it only through a floating-point exception, the result can instead be a NaN string. Very small subnormal inputs can cause a platform-dependent range error. The wrapper returns RANGE for a reported range error and the empty string for another reported error. It checks errno, not floating-point exception flags. Validate the input range rather than relying on one particular error string.

Examples

The approximate examples describe the numeric value; the returned string may contain more digits.

Source

source/functions.c registers asin and implements function_asin through the shared math-function and error-return macros. include/functions.h defines argument conversion and formatting. The C/POSIX arc sine specification defines radians, the domain, and library error reporting.