Question about acceleration and deceleration of linuxCNC linear movement

Hello, everyone.
In the "tpUpdateCycle" function in the "tp.c" file, the calculation of the acceleration phase is done with the "tpCalculateRampAccel" function and the "tpUpdateDistFromAccel" function, but I can't see where the calculation of the deceleration phase is done.

Sorry, I looked into the function "tcUpdateDistFromAccel" again, and when a line segment is added and the final velocity of the segment is 0, it should be a decelerated displacement.
This seems to mean that I have to add three displacements to do acceleration, uniform velocity and deceleration

Correct, Linuxcnc accellerates at max velocity until it reaches requested velocity, then decellerates at the same rate to get to the end point accelleration. If you graph this in halscope, you will see the classic trapezoid. 

There are a few other factors that come into play regarding segment length and the look ahead to the next segment in the real world.