如何在Python中将偏移量/指针设置为列表/数组？

Question

Ironically I have made this program successfully in x86 ASM but I'm having major trouble with implementing it in Python.

I have only just started learning a high level language. Here is a snippet:

rn_table = [0x63, 0x06, 0xF0, 0x23, 0xF8, 0xE5, 0xA8, 0x01, 0xC1, 0xAE, 0x7F, 0x48,
0x7B, 0xB1, 0xDC, 0x09, 0x22, 0x6D, 0x7D, 0xEE, 0x9D, 0x58, 0xD5, 0x55, 0x24, 0x39, 0x7A, 0xDF,
0x8E, 0x54, 0x6C, 0x1B, 0xC0, 0x0B, 0xD0, 0x43, 0xD8, 0x9A, 0x47, 0x5D, 0x21, 0x02, 0x17, 0x4B,
0xDB, 0x11, 0xAF, 0x70, 0xCD, 0x4D, 0x34, 0x49, 0x72, 0x91, 0x2D, 0x62, 0x97, 0x59, 0x45, 0xF7,
0x6E, 0x46, 0xAA, 0x0A, 0xA3, 0xC8, 0x31, 0x92, 0x38, 0xFA, 0xD4, 0xE6, 0xCB, 0xF3, 0xDE, 0x6B,
0xBB, 0xF1, 0x1C, 0x3C, 0xD6, 0xAD, 0xB2, 0xA9, 0xDD, 0x57, 0x42, 0x95, 0x0C, 0x79, 0x25, 0x1F,
0xBC, 0xE7, 0xAC, 0x5B, 0x83, 0x28, 0x76, 0xF2, 0x18, 0xDA, 0x87, 0xA1, 0x61, 0x6F, 0xBE, 0x5A,
0x5E, 0x51, 0xEF, 0xB0, 0xC9, 0x15, 0x74, 0x89, 0xBD, 0xD1, 0xA2, 0x75, 0xD7, 0x99, 0x85, 0x4C,
0x4F, 0xD2, 0xBF, 0x4A, 0x20, 0x08, 0x56, 0xA0, 0x50, 0x3A, 0x67, 0x26, 0x41, 0x33, 0xB7, 0xBA,
0xFB, 0x30, 0xCF, 0x7C, 0x84, 0x2C, 0x32, 0xE9, 0x1D, 0x16, 0x82, 0x78, 0xA4, 0x80, 0x65, 0x5F,
0x0E, 0x27, 0xB9, 0x19, 0xC3, 0xA7, 0xB6, 0x00, 0x3B, 0xFC, 0x88, 0xE1, 0xC6, 0x93, 0xFE, 0x8B,
0xD9, 0xB8, 0x13, 0x69, 0x2F, 0x64, 0x12, 0x37, 0xFD, 0x77, 0xE2, 0xB5, 0x04, 0xE0, 0x1A, 0x8C,
0x8F, 0xB4, 0xCC, 0xF9, 0x60, 0xEB, 0x29, 0xE3, 0x90, 0xA5, 0x68, 0x3D, 0x81, 0x73, 0x3F, 0xAB,
0x7E, 0xB3, 0x0F, 0xCE, 0xC4, 0x35, 0x94, 0x96, 0x86, 0x71, 0xD3, 0x2A, 0xE4, 0x9F, 0x9C, 0xEC,
0x4E, 0x14, 0xF5, 0xEA, 0x40, 0xA6, 0xF6, 0x03, 0x98, 0xC5, 0x07, 0xF4, 0x2B, 0xC2, 0x3E, 0xE8,
0x9B, 0x36, 0x53, 0x2E, 0x8D, 0x0D, 0x52, 0x10, 0x66, 0x1E, 0xED, 0x8A, 0x44, 0x9E, 0x05, 0xFF,
0x5C, 0xC7, 0x6A, 0xCA, 0x00, 0x0C, 0x12, 0x19, 0x21, 0x27, 0x2D, 0x35, 0x3D, 0x49, 0x51, 0x5A,
0x62, 0x69, 0x72, 0x7A, 0x83, 0x8B, 0x94, 0x9D, 0xA5, 0xAB, 0xB2, 0xB9, 0xC1, 0xC9, 0xD2, 0xD9,
0xDE, 0xE3, 0xE8, 0xED, 0xF5]


cluck = 16
clevel = 12
enemy_level = 10

crit_pc = (cluck + clevel - enemy_level) / 4

offset2 = 0
offset3 = 0

rnd1 = 0
rnd2 = 0
rnd0 = 0

crit_rnd = 0

lookups = [0, 0, 0, 0, 0, 0, 0, 0]
lookup_main = 0


def rng_go():
    global lookup_main
    lookups[lookup_main] = offset2      # lookup_main chooses lookups item. position = offset2
    lookups[lookup_main] += 1           # increase the lookups chosen value by 1 (previously offset2)
    rn_table[offset2] = rnd1            # choose value from rn_table, position of value is offset2

    if crit_pc == 0:
        print "No critical\n"
    lookup_main += 1                    # increment lookup_main by 1
    lookup_main = lookup_main and 7     # check lookup_main < 8
    lookups[lookup_main] = offset3      # lookup_main chooses another lookups item. position = offset3
    lookups[lookup_main] += 1           # increase lookups chosen value by 1
    rn_table[offset3] = rnd2            # choose value from rn_table, position of value is offset3
    # calculate critical%
    rnd2 * 256
    rnd0 = rnd1 or rnd2
    rnd0 = rnd0 and 65535
    crit_rnd = ((rnd0 * 99) / 65535) + 1
    if crit_pc >= crit_rnd:
        print "Critical hit success!\n"
        print "crit_rnd: %d \t crit_pc: %d" % (crit_rnd, crit_pc)
        print "rnd1: %d \t rnd2: %d" % (rnd1, rnd2)
        print "lookups: %r" % (lookups)
    else:
        print "No critical\n"
        print "crit_rnd: %d \t crit_pc: %d" % (crit_rnd, crit_pc)
        print "rnd1: %d \t rnd2: %d" % (rnd1, rnd2)
        print "lookups: %r" % (lookups)
rng_go()

I want to use lookup_main as a kind of pointer to the lookups list. So, position 0 in lookups is 0. Position 1 is 2, and so on.

I want to therefore increase this pointer/offset, but I am clearly doing it wrong.

How can I increment the offset to the list? I don't want to directly manipulate any numbers in the list. I just want to change the offset.

Actually, now that I think about it... it seems I'm stuck thinking in the 'Assembly' way of doing things >.< Hope this goes away... I'm unable to think 'big picture' >.<''''

The (dis)assembly that works is like:

lw r3,0x00d4(r28)      # load word from 80062e18 = offset1
lui r2, 0x8006
addiu r2,r2,0x2e10      # 80062e10
addu r3,r3,r2         # 80062e10 + (word from 80062e18 as offset)
lbu r2,0x0(r3)         # load byte from 80062e10(offset1) = offset2
nop

addiu r4,r2,0x01      
andi r2,r2,0xff
sb r4,0x0(r3)         # increment by 1 and store

lui r1,0x8008
addu r1,r1,r2         # 80083084
lbu r2,0x3084(r1)      # load byte from 80083084(offset2) = rnd1
jr r31
nop

lw r3,0x0008(r28)      # load word from 80062d4c
nop

addiu r4,r3,0x01      # increment by 1

andi r3,r3,0x07         # AND 7 (check that value < 8)
sw r4,0x08(r28)         # store incremented value back to 8062d4c


beq r3,r0,0x14c18      # if crit% = 0 then no critical
addu r16,r2,r0         # move rnd1
jal 0x14b54
nop

lw r2,0xd4(r28)         # load word from 80062e18
nop
addiu r2,r2,0x01      # increment by 1
andi r2,r2,0x07         # AND with 7 (check that value < 8) = offset2
sw r2,0xd4(r28)         # store in 80026e18
jr r31
nop

jal 0x14b70
nop

lw r3,0xd4(r28)         # load word from 80062e18 = offset3
lui r2,0x8006
addiu r2,r2,0x2e10      
addu r3,r3,r2         
lbu r2,0x0(r3)         # load byte from 80062e10(offset3) = offset4
nop

addiu r4,r2,0x01      
andi r2,r2,0xff         
sb r4,0x0(r3)         # increment byte by 1 and store in 80062e11

lui r1,0x8008         
addu r1,r1,r2         
lbu r2,0x3084(r1)      # load byte from 80083084(offset4) = rnd2
jr r31
nop

andi r2,r2,0xff         
sll r2,r2,0x08         # rnd2 * 256
andi r3,r16,0xff      
or r2,r3,r2         # rnd1 OR rnd2 (combine rnd1 and rnd2) = rnd0
lw r31,0x14(r29)
lw r16,0x10(r29)
addiu r29,r29,0x18
jr r31
nop

lw r31,0x10(r29)
andi r2,r2,0xffff      # take 2 bytes of rnd0
jr r31
addiu r29,r29,0x18


## calculate crit_rnd for which to compare against crit% ##

lui r4,0x8000
ori r4,r4,0x8001      
andi r2,r2,0xffff      
sll r3,r2,0x01         
addu r3,r3,r2         
sll r2,r3,0x05         ## Just: crit_rnd = ((rnd0 * 99) / 65535) + 1
addu r3,r3,r2         
mult r3,r4         
addu r2,r5,r3         
sra r2,r2,0x0f         
sra r3,r3,0x1f         
subu r2,r2,r3         
lw r31,0x10(r29)
addiu r2,r2,0x01      
jr r31
addiu r29,r29,0x0018      

slt r2,r16,r2         
bne r2,r0,0xb0888      # if crit% >= crit_rnd then critical hit success
nop 

Answer 1

List access in Python is not very complicated. The Python tutorial has some decent introductory examples.

To read a value from a list, just provide a suitable index:

list_name[index]

To assign the value to a variable, just use an assignment statement:

some_var = list_name[index]

To write a value into a list, just turn the assignment statement around:

list_name[index] = some_value

I think you had a few of your assignments backwards.

The other major issue you had was due to using the logical or and and operators instead of the bitwise | and & operators. The former won't do what you want, in most cases.

Here's some fixed code. I've omitted the offset values, since they're not really needed:

rnd1 = rn_table[lookups[lookup_main]]
lookups[lookup_main] += 1

lookup_main += 1
lookup_main &= 7   # doing %= 8 might be more clear

rnd2 = rn_table[lookups[lookup_main]]
lookups[lookup_main] += 1

rnd2 *= 256        # or use <<= 8 to left shift instead of multiplying

rnd0 = rnd1 | rnd2
rnd0 &= 65535      # this step should be unnecessary

Two values in the lookups list will be incremented by running this, which I assume is a desired side effect. lookup_main will also be incremented once, wrapping around if it goes above 7.

As I commented in the code, some of the bitwise operations might be more clear if you used different operators (with the same effects). This is a style judgement, so your mileage may vary.

Using the modulus operator % in the logic to increment lookup_main may be a bit clearer that you're forcing it to wrap around to zero if it reaches 8. Similarly, left shifting rnd2 with the << operator may be more clear than doing a multiplication. I'd also suggest using hexidecimal for any constants you use in bitwise operations (so 0xFFFF instead of 65535 ).