MEINVF32 MRa, MRb
32-Bit Floating-Point Reciprocal Approximation
Operands
MRa
CLA floating-point destination register (MR0 to MR3)
MRb
CLA floating-point source register (MR0 to MR3)
Opcode
LSW: 0000 0000 0000 bbaa
MSW: 0111 1111 0000 0000
Description
This operation generates an estimate of 1/X in 32-bit floating-point format accurate to
approximately 8 bits. This value can be used in a Newton-Raphson algorithm to get a
more accurate answer. That is:
Ye = Estimate(1/X);
Ye = Ye*(2.0 - Ye*X);
Ye = Ye*(2.0 - Ye*X);
After two iterations of the Newton-Raphson algorithm, you will get an exact answer
accurate to the 32-bit floating-point format. On each iteration the mantissa bit accuracy
approximately doubles. The MEINVF32 operation will not generate a negative zero,
DeNorm or NaN value.
MRa = Estimate of 1/MRb;
Flags
This instruction modifies the following flags in the MSTF register:
Flag
TF
ZF
NF
LUF
LVF
Modified
No
No
No
Yes
Yes
The MSTF register flags are modified as follows:
• LUF = 1 if MEINVF32 generates an underflow condition.
• LVF = 1 if MEINVF32 generates an overflow condition.
Pipeline
This is a single-cycle instruction.
Example
; Calculate Num/Den using a Newton-Raphson algorithum for 1/Den
; Ye = Estimate(1/X)
; Ye = Ye*(2.0 - Ye*X)
; Ye = Ye*(2.0 - Ye*X)
;
_Cla1Task1:
MMOV32 MR1, @_Den ; MR1 = Den
MEINVF32 MR2, MR1 ; MR2 = Ye = Estimate(1/Den)
MMPYF32 MR3, MR2, MR1 ; MR3 = Ye*Den
MSUBF32 MR3, #2.0, MR3 ; MR3 = 2.0 - Ye*Den
MMPYF32 MR2, MR2, MR3 ; MR2 = Ye = Ye*(2.0 - Ye*Den)
MMPYF32 MR3, MR2, MR1 ; MR3 = Ye*Den
|| MMOV32 MR0, @_Num ; MR0 = Num
MSUBF32 MR3, #2.0, MR3 ; MR3 = 2.0 - Ye*Den
MMPYF32 MR2, MR2, MR3 ; MR2 = Ye = Ye*(2.0 - Ye*Den)
|| MMOV32 MR1, @_Den ; Reload Den To Set Sign
MNEGF32 MR0, MR0, EQ ; if(Den == 0.0) Change Sign Of Num
MMPYF32 MR0, MR2, MR0 ; MR0 = Y = Ye*Num
MMOV32 @_Dest, MR0 ; Store result
MSTOP ; end of task
See also
Control Law Accelerator (CLA)
622
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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