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Instructions
EISQRTF32 RaH, RbH
32-bit Floating-Point Square-Root Reciprocal Approximation
Operands
RaH
floating-point destination register (R0H to R7H)
RbH
floating-point source register (R0H to R7H)
Opcode
LSW: 1110 0110
1001 0010
MSW: 0000 0000
00bb baaa
Description
This operation generates an estimate of 1/sqrt(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/sqrt(X));
Ye = Ye*(1.5 - Ye*Ye*X/2.0)
Ye = Ye*(1.5 - Ye*Ye*X/2.0)
After 2 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 EISQRTF32 operation will not generate a negative zero,
DeNorm or NaN value.
RaH = Estimate of 1/sqrt (RbH)
Flags
This instruction modifies the following flags in the STF register:
Flag
TF
ZI
NI
ZF
NF
LUF
LVF
Modified
No
No
No
No
No
Yes
Yes
The STF register flags are modified as follows:
•
LUF = 1 if EISQRTF32 generates an underflow condition.
•
LVF = 1 if EISQRTF32 generates an overflow condition.
Pipeline
This is a 2 pipeline cycle (2p) instruction. That is:
EINVF32
RaH, RbH
; 2 pipeline cycles (2p)
NOP
; 1 cycle delay or non-conflicting instruction
; <-- EISQRTF32 completes, RaH updated
NOP
Any instruction in the delay slot must not use RaH as a destination register or use RaH
as a source operand.
SPRUEO2A – June 2007 – Revised August 2008
Instruction Set
49
Summary of Contents for TMS320C28 series
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