Fix tinyram prelude, tinyram read from aux input.

[tkerber]

When trying to get a simple example (attached) to function with the demo_ram_ppzksnark executable, I encountered a problem that the read opcode wasn't functioning as specified.

Two mistakes I noticed there were:
a) the flag on read was being incorrectly set when read_not1 was != 1, while it should be when read_not1 is != 0 (this matches the r1cs constraints one read_not1, and further correctly sets the flag for tape 0 and not for tape 1).
b) Fixing this resulted in values being consumed from tape 1 regardless of opcode, as the tape reading did not expicitly check for a read opcode.

Unrelated during my debugging of this, I found that the prelude generation of tinyram increments by log(w)/8. This is clearly a mistake, as w is already a size in bits.

---

The example I was using which did not work before:

command:

$ libsnark/demo_ram_ppzksnark --assembly simple.s --processed_assembly simple.proc --architecture_params simple.params --computation_bounds simple.bounds --primary_input simple.input --auxiliary_input simple.input

simple.s:

; TinyRAM V=1.00 W=32 K=8

; Simple test program. Read from the input tape, from the aux tape, and check
; if they're equal.

; begin prelude
store.w 0, r0
mov r0, 2147483648
read r1, 0
cjmp 7
add r0, r0, 4
store.w r0, r1
jmp 2
store.w 2147483648, r0
; end prelude
load.w r0, 2147483648 ; The first word of the primary input tape should be here. (memory 0x8000 0000, this is 1<<(w-1))
read r1, 1
xor r0, r0, r1 ; r0 is 0 iff r0 = r1
answer r0

simple.proc

store.w
1
0
0
0
mov
1
0
0
2147483648
read
1
0
0
1
cjmp
1
0
0
7
add
1
0
0
4
store.w
0
1
0
0
jmp
1
0
0
2
store.w
1
0
0
2147483648
load.w
1
0
0
2147483648
read
1
1
0
1
xor
0
0
0
1
answer
0
0
0
0

simple.params:

32
8

simple.bounds:

32
32
32

simple.input:

42

---

P.S. Is there a public assember for TinyRAM? I had to write the processed assembly by hand, and while it'd be easy enough to write one, I'd prefer to avoid duplicating effort.