The SHT performance tests without polarization for Healpy, fastSHT-CPU, and fastSHT-GPU, with an N _side that varies from 32 to 1024, ﹩{{\ell }}_{\max }=3{N}_{\mathrm{side}}-1﹩, and N _iter = 3. The numbers of maps are 250 to 4000 (bottom to top, respectively), which are determined by the GPU memory limit at the highest resolution in each panel. The colored bars (corresponding to the left y-axis) give the time costs per sky map per pixel, and the stars and dots (corresponding to the right y-axis) show fastSHT-CPU’s and fastSHT-GPU's acceleration factors relative to Healpy, respectively.