"TMS320C55x DSP Library DSPLIB Programmer's Reference"

lognThe coefficients Bi used in the calculation are derived from the Ci as follows:B0 Q30 1581d 0062DhB1 Q14 16381d 03FFDhB2 Q15 –16298d 0C056hB3 Q16 20693d 050D5hB4 Q17 –24950d 09E8AhB5 Q18 21677d 054ADhB6 Q19 –9130d 0DC56hExampleBenchmarksSee examples/log_2 subdirectory(preliminary)Cycles † Core: 36 * nxOverhead: 37Code size(in bytes)166† Assumes all data is in on-chip dual-access RAM and that there is no bus conflict due to twiddletable reads and instruction fetches (provided linker command file reflects those conditions).lognFunctionBase e Logarithm (natural logarithm)ushort oflag = logn (DATA *x, LDATA *r, ushort nx)(defined in logn.asm)Argumentsx[nx]r[nx]nxoflagPointer to input vector of size nx.Pointer to output data vector (Q31 format) of size nx.Length of input and output data vectorsOverflow flag. If oflag = 1, a 32-bit overflow has occurred. If oflag = 0, a 32-bit overflow has not occurred.DescriptionComputes the log base e of elements of vector x using Taylor series.Algorithm for (i 0; i nx; i ) y(i) log nx(i) where –1 x(i) 1Overflow Handling MethodologyNo scaling implemented for overflow preventionSpecial Requirements Special RequirementsnoneFunction Descriptions4-67