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Diffstat (limited to 'private/crt32/misc/alpha/extzv.s')
| -rw-r--r-- | private/crt32/misc/alpha/extzv.s | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/private/crt32/misc/alpha/extzv.s b/private/crt32/misc/alpha/extzv.s new file mode 100644 index 000000000..fb73dfb8e --- /dev/null +++ b/private/crt32/misc/alpha/extzv.s @@ -0,0 +1,83 @@ + #++ + # Copyright 1991, Digital Equipment Corporation + # + # int ots_extzv(char *addr, int position, unsigned size) + # + # Arbitrary unsigned bitfield extraction + # + # Special conventions: No stack space, r0, r16-r18 and r26-r28 ONLY, + # no linkage pointer required. + # (Warning: The auto-loader potentially takes some regs across + # the call if this is being used in a shared lib. environment.) + # + # See also: ots_extv (just uses sra in place of srl in some cases...) + # + # 001 16 Aug 1991 KDG Initial version + # + # 002 4 Sep 1991 KDG Bugfix/improvements + # + # 003 19 May 1992 KDG Changes for common VMS/OSF sources + # + # 004 22 Sep 1992 KDG Add case-sensitive name + # + # 005 26 Jan 1993 KDG Add underscore + +#include "ots_defs.hs" + + # + # Totally general field extract - arbitrary run-time field of 0-64 bits + # at an unknown alignment target. + # + # Conceptually, this operation takes a 67 bit bit-address, which is the sum + # of a byte-aligned memory address and the bit offset (which is signed). + # + # +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + # | | | | | | | | | | | | | | | | | | | | | | | | | |.|.|.|Q|L|W|B| + # +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + # | | | | | | | | | | | | | | | | | | | | | | | | | | |.|.|.|b|b|b| + # +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + # + # Inputs: + # r16 - input address + # r17 - input bit offset + # r18 - input size + # + # This is based on the code GEM generates when not using an out-of-line + # routine. + # + .globl _OtsFieldExtractUnsigned + .ent _OtsFieldExtractUnsigned +_OtsFieldExtractUnsigned: + .set noat + .set noreorder + .frame sp,0,r26 + sra r17, 3, r27 # get byte part of bit offset (signed!) + ble r18, zero # check for zero size - no memory access + addq r16, r27, r16 # add to initial base addr. + ldq_u r0, (r16) # start load first or only quadword + and r16, 7, r27 # get byte-in-quadword of first bit + and r17, 7, r17 # get bit-in-byte from bit offset + s8addq r27, r17, r17 # form the true bit offset in the quadword + addq r17, r18, r27 # get bit offset of bit following field + cmpule r27, 64, r28 # if <=64, field is contained in 1 quadword + beq r28, double # handle double case if not + # common case - fall through, load result hopefully already available +single: negq r27, r27 # <5:0> = bits for right shift + sll r0, r27, r0 # move to high bits + addq r27, r17, r27 # bits for left shift + srl r0, r27, r0 # and shift into final position + ret r31, (r26) +double: ldq_u r28, 8(r16) # load second quadword + srl r0, r27, r0 # move top piece over + negq r27, r27 # get shift bits for piece in 2nd word + sll r28, r27, r28 # move field in 2nd lw to high bits + bis r0, r28, r0 # form final value + negq r18, r27 # <5:0> = bits for right shift + srl r0, r27, r0 # and shift into final position + ret r31, (r26) +zero: mov 0, r0 # zero-sized field extracts return 0 + ret r31, (r26) + + .set at + .set reorder + .end _OtsFieldExtractUnsigned |