When you're willing to make an approximation you can come up with all sorts of very short functions for common operations. Here's one from my project, which ta

When you're willing to make an approximation you can come up with all sorts of very short functions for common operations. Here's one from my project, which takes an integer x and calculates a (float) log2(x) in an absurdly low number of operations. static inline float x264_log2( uint32_t x ) { int lz = __builtin_clz( x ); return x264_log2_lut[(x<<lz>>24)&0x7f] + x264_log2_lz_lut[lz]; } const float x264_log2_lut[128] = { 0.00000, 0.01123, 0.02237, 0.03342, 0.04439, 0.05528, 0.06609, 0.07682, 0.08746, 0.09803, 0.10852, 0.11894, 0.12928, 0.13955, 0.14975, 0.15987, 0.16993, 0.17991, 0.18982, 0.19967, 0.20945, 0.21917, 0.22882, 0.23840, 0.24793, 0.25739, 0.26679, 0.27612, 0.28540, 0.29462, 0.30378, 0.31288, 0.32193, 0.33092, 0.33985, 0.34873, 0.35755, 0.36632, 0.37504, 0.38370, 0.39232, 0.40088, 0.40939, 0.41785, 0.42626, 0.43463, 0.44294, 0.45121, 0.45943, 0.46761, 0.47573, 0.48382, 0.49185, 0.49985, 0.50779, 0.51570, 0.52356, 0.53138, 0.53916, 0.54689, 0.55459, 0.56224, 0.56986, 0.57743, 0.58496, 0.59246, 0.59991, 0.60733, 0.61471, 0.62205, 0.62936, 0.63662, 0.64386, 0.65105, 0.65821, 0.66534, 0.67243, 0.67948, 0.68650, 0.69349, 0.70044, 0.70736, 0.71425, 0.72110, 0.72792, 0.73471, 0.74147, 0.74819, 0.75489, 0.76155, 0.76818, 0.77479, 0.78136, 0.78790, 0.79442, 0.80090, 0.80735, 0.81378, 0.82018, 0.82655, 0.83289, 0.83920, 0.84549, 0.85175, 0.85798, 0.86419, 0.87036, 0.87652, 0.88264, 0.88874, 0.89482, 0.90087, 0.90689, 0.91289, 0.91886, 0.92481, 0.93074, 0.93664, 0.94251, 0.94837, 0.95420, 0.96000, 0.96578, 0.97154, 0.97728, 0.98299, 0.98868, 0.99435, }; /* Avoid an int/float conversion. */ const float x264_log2_lz_lut[32] = { 31,30,29,28,27,26,25,24,23,22,21,20,19,18,17,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1,0 }; The resulting asm, just 7 instructions: bsr ecx, eax xor ecx, 0x1f movss xmm0, [ecx*4+x264_log2_lz_lut] shl eax, cl shr eax, 0x18 and eax, 0x7f addss xmm0, [eax*4+x264_log2_lut]