Motorola DSP Developer's Kit

log-c.asm

Y = mot###_log( X )

Description

This function returns the natural logarithm elements of complex input vector X.

Input/Output

Input: Complex vector X

Output: Complex vector Y

Algorithm

log(a+bi) = log(sqrt(a^2 + b^2))+angle(a,b)*i

If an absolute result is needed, the real data of the result should be scaled up by 32 and imaginary data of the result should be scaled up by 4. Please refer to the algorithms used in log-r.asm and angle-c.asm.

Memory & Register

Memory allocation:

In X memory:

• XYZ is used as a temporary variable area

+0--X  +1--Y  +2--log(sqrt(Xr[i]*Xr[i]+Xi[i]*Xi[i])/32(or 16)

ATANTAB stores the atan table

Y memory:

• $10 is used for the coefficient of polynomial
• X:IN_REAL stores the start address of the real input data of vector A
• Y:IN_IMAG stores the start address of the imaginary input data of vector A
• X:IN_REAL stores the start address of the real output data of vector A
• Y:IN_IMAG stores the start address of the imaginary output data of vector A

Register usage:

• R0 points to the input vector area
• R1 is used for the index of coefficient
• R2 is used for loopnum

In the case of dsp56300, loopnum = 22

In the case of dsp56600, loopnum = 14

• R3 points to the start address of table ATANTAB
• R4 is used for temporary storage
• N4 is used for shift bits

6 for dsp56300

5 for dsp56600

• R5 points to the output vector area
• R6 stores the length of the input vector
• R7 points to the temporary variable area XYZ

Assumes M{0...7} = $ffff

Status Register

The assembly function log-c.asm does not explicitly set any status registers/bits during the function execution.

Data Size Limit

The length of vector X can't be larger than the continuous available data memory size.

Data Range Limit

The value of input vector X must be between -1.0 and +1.0.

Precision

In the case of DSP563, precision is 16 bits.

In the case of DSP566, precision is 12 bits.

log-r.asm

log10-r.asm