Saturday, 31 May 2008

An Improved '88 Quick-scanner

After reading how Paul Kline's slowQscan achieves extra scans, I wondered how well a similar technique would work in '88 Standard Redcode. Previously published '88 quick-scanners include:
Using Kline's technique 36 scans are possible in 48 instructions:

qfirst equ (qp2+2*qstep)
qdist  equ qfirst+111
qstep  equ 222

qi  equ 7                       
qr  equ 7

qbomb   dat <qi/2-qi*qr,   <qi*qr-qi/2

qa  equ qstep*16
qb  equ qstep*5+2
qc  equ qstep*10
qd  equ qstep*2
qe  equ qstep*1

qgo     cmp qdist+qc,      qfirst+qc
jmp qfast,         <qa
cmp qdist+qe+qd,   qfirst+qe+qd
qp1     jmp <qfast,        <qc
qp2     cmp qdist,         qfirst
qp3     jmp qskip,         <qe

cmp qdist+qb,      qfirst+qb
q1      djn qfast,         #qp1

cmp qdist+qd+qc,   qfirst+qd+qc
jmp qslow,         <qfirst+qd+qc+4
cmp qdist+qd+qb,   qfirst+qd+qb
x1      jmp qslow,         <q1
cmp qdist+qc+qc,   qfirst+qc+qc
q2      djn qslow,         #qp2
cmp qdist+qd,      qfirst+qd
jmp qslow,         <qfast
cmp qdist+qa,      qfirst+qa
jmp q1,            <q1

cmp qdist+qa+qd,   qfirst+qa+qd
jmp x1,            <q1
cmp qdist+qc+qb,   qfirst+qc+qb
jmp q2,            <q1
cmp qdist+qe+qd+qc,qfirst+qe+qd+qc
jmp qslower,       <qfirst+qe+qd+qc+4
cmp qdist+qe+qd+qb,qfirst+qe+qd+qb
jmp qslower,       <q1
cmp qdist+qe+qc+qc,qfirst+qe+qc+qc
jmp qslower,       <q2
cmp qdist+qd+qd+qc,qfirst+qd+qd+qc
q3      djn qslower,       #qp3
cmp qdist+qe+qc,   qfirst+qe+qc
jmp <qfast,        <q2
cmp qdist+qd+qd,   qfirst+qd+qd
jmp <qfast,        <q3
cmp qdist+qd+qd+qb,qfirst+qd+qd+qb
slt <q3,           <q1

jmz pgo,           qdist+qe+qd+qc+10

qslower add @q3,           @qslow
qslow   add @q2,           qkil
qfast   add @q1,           @qslow

qskip   cmp <qdist+qstep+50, @qkil
jmp qloop,         <1234

add #qdist-qfirst, qkil
qloop   mov qbomb,         @qkil
qkil    mov <qfirst+qstep+50, <qfirst
sub #qi,           @qloop
djn qloop,         #qr+2

end qgo

Wednesday, 14 May 2008

x^n (mod CORESIZE) in Redcode

The following code implements the binary method to calculate x^n (mod CORESIZE) in Redcode. For calculations with n > 13, the binary method out-performs a simple loop.
power     mov    #1,             _powerr
_powloop mov.b _powern, temp
mod #2, temp
seq.b temp, #0
mul.b _powerx, _powerr
mul.b _powerx, _powerx
div #2, _powern
jmn _powloop, _powern

_powern dat n
_powerx dat x
_powerr dat 1