#++
# Copyright 1991, 1994, Digital Equipment Corporation
#
# ots_zero(char *dstptr, long dstlen)
#
# Zero dstlen bytes of memory at *dstptr
#
# Special conventions: No stack space, r16-r17 and r27-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.)
#
# This is a GEM support routine for zeroing a region of memory. It is
# basically idential to BSD's bzero, though it has limited register
# convensions to allow it to work better with compiled code. (Note that
# this is just a stripped down version of ots_fill.)
#
# This is optimized for extremely high performance both for small and
# large blocks. In order to reduce overhead for small cases, they are
# retired as quickly as possible, more case analysis is reserved
# for cases which will do more.
#
# This version of OTS_ZERO provides longword granularity for Alpha.
#
# 012 30 Aug 1994 WBN Longword granularity version based on
# OTS_ZERO_ALPHA.M64 edit 011.
#--
#include "ots_defs.hs"
# r16 = dst
# r17 = len
# destroys r16-r17, r27-r28
.globl _OtsZero
.ent _OtsZero
_OtsZero:
.set noat
.set noreorder
.frame sp,0,r26
.prologue 0
beq r17, done # No memory refs if len=0
subq r17, 4, r28 # Length-4
and r16, 3, r27 # Dst alignment (0-3)
andnot r16, 3, r16 # LW aligned dst pointer
addq r27, r28, r17 # Alignment + length - 4
bge r28, geq4 # Lengths >= 4 may not need load
ldl r28, (r16) # Load first LW of dst
bgt r17, double # Skip if it crosses to next LW
addq r17, 4, r17 # Find endpoint within LW
mskql r28, r27, r27 # Clear from startpoint thru 7
mskqh r28, r17, r28 # Clear from 0 to endpoint
or r28, r27, r27 # Combine dest parts
stl r27, (r16)
ret r31, (r26)
double: mskql r28, r27, r28 # Clear from startpoint in first LW
ldl r27, 4(r16) # Load second LW of dst
stl r28, (r16)
mskqh r27, r17, r27 # Clear up to endpoint in second LW
stl r27, 4(r16)
ret r31, (r26)
# Come here if length to be zeroed is >= 4.
# r16-> dst aligned to LW
# r17 = alignment + length - 4
# r27 = dst alignment within LW
# r28 = length-4
#.align quad
geq4: and r16, 4, r28 # Which LW in QW to store first?
beq r17, simple # Go handle single aligned LW
bne r28, longs # Go use QW stores
quad: subq r17, 4, r17 # Does dest end in first QW?
blt r17, shortq # Ends within first QW
beq r27, wh_qw # Store a whole QW
ldq r28, (r16) # Load first QW of dest
mskql r28, r27, r27 # Clear from startpoint
wh_qw: stq r27, (r16) # Store first QW of dest
br r31, join # Go clear rest of string
simple: stl r31, (r16) # Single aligned LW
ret r31, (r26)
shortq: ldq r28, (r16) # Load QW of dest
mskql r28, r27, r27 # Clear from startpoint thru 7
mskqh r28, r17, r28 # Clear from 0 up to endpoint
or r28, r27, r27 # Merge
stq r27, (r16) # Store
ret r31, (r26)
longs: beq r27, wh_lw # Store a whole LW
ldl r28, (r16) # Load first LW of dest
mskql r28, r27, r27 # Clear from startpoint
wh_lw: stl r27, (r16) # Store first LW of dest
join: subq r17, 32, r17 # At least 4 more quadwords?
and r17, 24, r27 # How many after multiple of 4?
bge r17, unroll # Taken branch for long strings
short: and r17, 7, r17 # How many odd bytes?
beq r27, last # Skip if no more whole QWs
stq_u r31, 8(r16) # Clear one...
subq r27, 16, r27 # Map 8/16/24 to -8/0/8
addq r16, 8, r16 # Update dest pointer
blt r27, last # Skip if no more whole QWs
#stall
stq_u r31, 8(r16) # Clear two...
addq r16, 8, r16 # Update dest pointer
nop
beq r27, last # Skip if no more whole QWs
stq_u r31, 8(r16) # Clear three...
addq r16, 8, r16 # Update dest pointer
last: beq r17, done # Finished if no odd bytes
ldq_u r27, 8(r16) # Load last QW of dst
subq r17, 4, r28 # More than a LW left?
andnot r16, 7, r16 # Clean pointer for STL
mskqh r27, r17, r27 # Clear up to endpoint
bgt r28, lastq # Go store a QW
stl r27, 8(r16) # LW store for last piece
done: ret r31, (r26)
lastq: stq r27, 8(r16) # QW store for last piece
ret r31, (r26)
unroll: stq_u r31, 8(r16) # Store 4 QWs per iteration
stq_u r31, 16(r16)
stq_u r31, 24(r16)
subq r17, 32, r17 # Decrement remaining count
stq_u r31, 32(r16)
addq r16, 32, r16 # Update dest pointer
bge r17, unroll # Repeat until done
br r31, short # Then handle leftovers
.set at
.set reorder
.end _OtsZero
