Rounding Operations

The functions ffloor, fceiling, fround, and ftruncate take a floating-point argument and return a floating-point result whose value is a nearby integer. ffloor returns the nearest integer below; fceiling, the nearest integer above; ftruncate, the nearest integer in the direction towards zero; fround, the nearest integer.

Function: ffloor float

This function rounds float to the next lower integral value, and returns that value as a floating-point number.

Function: fceiling float

This function rounds float to the next higher integral value, and returns that value as a floating-point number.

Function: ftruncate float

This function rounds float towards zero to an integral value, and returns that value as a floating-point number.

Function: fround float

This function rounds float to the nearest integral value, and returns that value as a floating-point number. Rounding a value equidistant between two integers returns the even integer.

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https://www.gnu.org/software/emacs/manual/html_node/elisp/Rounding-Operations.html