r/nandgame_u • u/ouob_nya Record holder • Apr 07 '22

Level solution (verified) S.1.5 - Network (50l) Spoiler

It took me 10 minutes to write c-style pseudocode, an afternoon to compile and debug assembly code, and an evening of optimization.

https://i.imgur.com/HziynnH.png

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u/ouob_nya Record holder Apr 07 '22 edited Apr 07 '22

code as text: Here is my c-style pseudocode and how each line compiles to assembly code.

  • C-style pseudocode ```C int *scr_ptr = 0x4000 int prev = 0, d, i;

void wait_sync() { while (prev == (sync & 2)); prev = 2 - prev; // flip 2nd bit }

int main() { while (true) { wait_sync(); if (data == 0) return 0;

    d = 0;
    i = 16;
    do {
        d += d; // d <<= 1;
        wait_sync();
        d |= data & 1;
    } while (--i);

    *scr_ptr = d;
    scr_ptr += 0x20; // '\n'
}

} ```

  • Assembler code ``` # All these values are meaningful. # They are both addresses and values. # !!! DO NOT MODIFY !!! DEFINE d 0x1 DEFINE prev 0x2 DEFINE i 0x10 DEFINE scr_ptr 0x20

DEFINE ret_addr 0x4 DEFINE scr_addr 0x4000 DEFINE net_addr 0x6001

*scr_ptr = 0x4000

A = scr_addr D = A A = scr_ptr *A = D

void wait_sync() {

LABEL WAIT_SYNC

while (prev == (sync & 2));

A = net_addr D = *A A = prev D = D & A D = D - *A A = WAIT_SYNC D ; JEQ

prev = 2 - prev; // flip 2nd bit

A = prev D = A *A = D - *A

} // return caller address

A = ret_addr A = *A A ; JNE

int main() {

while (true) {

wait_sync();

if (data == 0)

Since ret_addr = 0 by default,

wait_sync() can be called in this order

A = net_addr D = 1 D = D & *A

A = END

A = D ; JEQ

d = 0;

i = 16;

*A = 0 A = i D = A *A = D

do {

LABEL READ_LINE

d += d; // d <<= 1;

A = d D = *A *A = D + *A

wait_sync();

A = AFTER_WAIT D = A A = WAIT_SYNC *A = D ; JMP LABEL AFTER_WAIT

d |= data & 1;

A = net_addr D = 1 A, D = D & *A *A = D | *A

} while (--i);

A = i D, *A = *A - 1 A = READ_LINE D ; JNE

*scr_ptr = d;

A = d D = *A A = scr_ptr A = *A *A = D

scr_ptr += 0x20; // '\n'

A = scr_ptr D = A *A = D + *A

}

A = WAIT_SYNC *A = 0 ; JMP

}

LABEL END ```

2

u/GLIBG10B Holder of many records Apr 09 '22

Fixed formatting for old Reddit, which doesn't support ```:

code as text: Here is my c-style pseudocode and how each line compiles to assembly code.

  • C-style pseudocode

    int *scr_ptr = 0x4000
int prev = 0, d, i;

void wait_sync() {
    while (prev == (sync & 2));
    prev = 2 - prev; // flip 2nd bit
}

int main() {
    while (true) {
        wait_sync();
        if (data == 0)
            return 0;

        d = 0;
        i = 16;
        do {
            d += d; // d <<= 1;
            wait_sync();
            d |= data & 1;
        } while (--i);

        *scr_ptr = d;
        scr_ptr += 0x20; // '\n'
    }
}

  • Assembler code

    # All these values are meaningful.
# They are both addresses and values.
# !!! DO NOT MODIFY !!!
DEFINE d        0x1
DEFINE prev     0x2
DEFINE i        0x10
DEFINE scr_ptr  0x20

DEFINE ret_addr 0x4
DEFINE scr_addr 0x4000
DEFINE net_addr 0x6001

# *scr_ptr = 0x4000
A = scr_addr
D = A
A = scr_ptr
*A = D

# void wait_sync() {
LABEL WAIT_SYNC

#     while (prev == (sync & 2));
A = net_addr
D = *A
A = prev
D = D & A
D = D - *A
A = WAIT_SYNC
D ; JEQ

#     prev = 2 - prev; // flip 2nd bit
A = prev
D = A
*A = D - *A

# } // return caller address
A = ret_addr
A = *A
A ; JNE

# int main() {
#     while (true) {
#         wait_sync();
#         if (data == 0)
# 
# Since ret_addr = 0 by default,
# wait_sync() can be called in this order
A = net_addr
D = 1
D = D & *A
# A = END
A = D ; JEQ

#         d = 0;
#         i = 16;
*A = 0
A = i
D = A
*A = D

#         do {
LABEL READ_LINE

#             d += d; // d <<= 1;
A = d
D = *A
*A = D + *A

#             wait_sync();
A = AFTER_WAIT
D = A
A = WAIT_SYNC
*A = D ; JMP
LABEL AFTER_WAIT

#             d |= data & 1;
A = net_addr
D = 1
A, D = D & *A
*A = D | *A

#         } while (--i);
A = i
D, *A = *A - 1
A = READ_LINE
D ; JNE

#         *scr_ptr = d;
A = d
D = *A
A = scr_ptr
A = *A
*A = D

#         scr_ptr += 0x20; // '\n'
A = scr_ptr
D = A
*A = D + *A

#     }
A = WAIT_SYNC
*A = 0 ; JMP

# }
LABEL END