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Import gmp 3.1

PPC630 (aka Power3) pipeline information:

Decoding is 4-way and issue is 8-way with some out-of-order capability.
LS1  - ld/st unit 1
LS2  - ld/st unit 2
FXU1 - integer unit 1, handles any simple integer instructions
FXU2 - integer unit 2, handles any simple integer instructions
FXU3 - integer unit 3, handles integer multiply and divide
FPU1 - floating-point unit 1
FPU2 - floating-point unit 2

Memory:		  Any two memory operations can issue, but memory subsystem
		  can sustain just one store per cycle.
Simple integer:	  2 operations (such as add, rl*)
Integer multiply: 1 operation every 9th cycle worst case; exact timing depends
		  on 2nd operand most significant bit position (10 bits per
		  cycle).  Multiply unit is not pipelined, only one multiply
		  operation in progress is allowed.
Integer divide:	  ?
Floating-point:	  Any plain 2 arithmetic instructions (such as fmul, fadd, fmadd)
		  Latency = 4.
Floating-point divide:
		  ?
Floating-point square root:
		  ?

Best possible times for the main loops:
shift:	      1.5 cycles limited by integer unit contention.
	      With 63 special loops, one for each shift count, we could
	      reduce the needed integer instructions to 2, which would
	      reduce the best possible time to 1 cycle.
add/sub:      1.5 cycles, limited by ld/st unit contention.
mul:	      18 cycles (average) unless floating-point operations are used,
	      but that would only help for multiplies of perhaps 10 and more
	      limbs.
addmul/submul:Same situation as for mul.