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                    POWERPC 32-BIT MPN SUBROUTINES


This directory contains mpn functions for various 32-bit PowerPC chips.


CODE ORGANIZATION

	directory	  used for
	================================================
	powerpc           generic, 604, 604e, 744x, 745x
	powerpc/750       740, 750, 7400, 7410


The top-level powerpc directory is currently mostly aimed at 604/604e but
should be reasonable on all powerpcs.



STATUS

The code is quite well optimized for the 604e, other chips have had less
attention.

Altivec SIMD available in 74xx might hold some promise, but unfortunately
GMP only guarantees 32-bit data alignment, so there's lots of fiddling
around with partial operations at the start and end of limb vectors.  A
128-bit limb would be a novel idea, but is unlikely to be practical, since
it would have to work with ordinary +, -, * etc in the C code.

Also, Altivec isn't very well suited for the GMP multiplication needs.
Using floating-point based multiplication has much better better performance
potential for all current powerpcs, both the ones with slow integer multiply
units (603, 740, 750, 7400, 7410) and those with fast (604, 604e, 744x,
745x).  This is because all powerpcs do some level of pipelining in the FPU:

603 and 750 can sustain one fmadd every 2nd cycle.
604 and 604e can sustain one fmadd per cycle.
7400 and 7410 can sustain 3 fmadd in 4 cycles.
744x and 745x can sustain 4 fmadd in 5 cycles.



REGISTER NAMES

The normal powerpc convention is to give registers as plain numbers, like
"mtctr 6", but on Apple MacOS X (powerpc*-*-rhapsody* and
powerpc*-*-darwin*) the assembler demands an "r" like "mtctr r6".  Note
however when register 0 in an instruction means a literal zero the "r" is
omitted, for instance "lwzx r6,0,r7".

The GMP code uses the "r" forms, powerpc-defs.m4 transforms them to plain
numbers according to what GMP_ASM_POWERPC_R_REGISTERS finds is needed.
(Note that this style isn't fully general, as the identifier r4 and the
register r4 will not be distinguishable on some systems.  However, this is
not a problem for the limited GMP assembly usage.)



GLOBAL REFERENCES

Linux non-PIC
	lis	9, __gmp_modlimb_invert_table@ha
	rlwinm	11, 5, 31, 25, 31
	la	9, __gmp_modlimb_invert_table@l(9)
	lbzx	11, 9, 11

Linux PIC (FIXME)
.LCL0:
	.long .LCTOC1-.LCF0
	bcl	20, 31, .LCF0
.LCF0:
	mflr	30
	lwz	7, .LCL0-.LCF0(30)
	add	30, 7, 30
	lwz	11, .LC0-.LCTOC1(30)
	rlwinm	3, 5, 31, 25, 31
	lbzx	7, 11, 3

AIX (always PIC)
LC..0:
	.tc __gmp_modlimb_invert_table[TC],__gmp_modlimb_invert_table[RW]
	lwz	9, LC..0(2)
	rlwinm	0, 5, 31, 25, 31
	lbzx	0, 9, 0

Darwin (non-PIC)
	lis	r2, ha16(___gmp_modlimb_invert_table)
	rlwinm	r9, r5, 31, 25, 31
	la	r2, lo16(___gmp_modlimb_invert_table)(r2)
	lbzx	r0, r2, r9
Darwin (PIC)
	mflr	r0
	bcl	20, 31, L0001$pb
L0001$pb:
	mflr	r7
	mtlr	r0
	addis	r2, r7, ha16(L___gmp_modlimb_invert_table$non_lazy_ptr-L0001$pb)
	rlwinm	r9, r5, 31, 25, 31
	lwz	r2, lo16(L___gmp_modlimb_invert_table$non_lazy_ptr-L0001$pb)(r2)
	lbzx	r0, r2, r9
------
	.non_lazy_symbol_pointer
L___gmp_modlimb_invert_table$non_lazy_ptr:
	.indirect_symbol ___gmp_modlimb_invert_table
	.long	0
	.subsections_via_symbols


For GNU/Linux and Darwin, we might want to duplicate __gmp_modlimb_invert_table
into the text section in this file.  We should thus be able to reach it like
this:

	blr	L0
L0:	mflr	r2
	rlwinm	r9, r5, 31, 25, 31
	addi	r9, r9, lo16(local_modlimb_table-L0)
	lbzx	r0, r2, r9



REFERENCES

PowerPC Microprocessor Family: The Programming Environments for 32-bit
Microprocessors, IBM document G522-0290-01, 2000.

PowerPC 604e RISC Microprocessor User's Manual with Supplement for PowerPC
604 Microprocessor, IBM document G552-0330-00, Motorola document
MPC604EUM/AD, 1998.

MPC7400 RISC Microprocessor User's Manual, Motorola document MPC7400UM/D,
rev 0, 3/2000.

The above are available online from

	http://chips.ibm.com/techlib/products/powerpc/manuals
	http://www.mot.com/PowerPC



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