li t0,0x20
csrs mstatush,t0 # Big-endian here we go!

li a7,4
la a0,msgentermessage
ecall # Prompt the user to type a message

li a7,8
la a0,message
li a1,17
ecall # Read the message

li a7,4
la a0,message
ecall # Print it back out

li a7,4
la a0,msgwait
ecall # Tell the user this might take a while...

# Count the message length and replace the null terminator with 0x80
la t0,message
li t1,0
1: lb t2,0(t0)
addi t0,t0,1
addi t1,t1,1
bnez t2,1b
addi t0,t0,-1
addi t1,t1,-1
li t2,0x80
sb t2,0(t0)
la t0,message+60
slli t1,t1,3
sw t1,0(t0)

li s0,0 # Round counter

# Copy message into w (full message since we're only doing the one chunk)
li t2,16
la t0,message
la t1,w
1: ld t3,0(t0) # Copy 2 words of message...
sd t3,0(t1) # ...to w
addi t0,t0,8
addi t1,t1,8
addi s0,s0,2
blt s0,t2,1b

# Wikipedia calls this "Extend the first 16 words into the remaining 48 words w[16..63] of the message schedule array"
1: la t0,w
sh2add t0,s0,t0
addi t0,t0,-60 # i-15
la t1,w
sh2add t1,s0,t1
addi t1,t1,-8 # i-2
la t2,w
sh2add t2,s0,t2
addi t2,t2,-64 # i-16
la t3,w
sh2add t3,s0,t3
addi t3,t3,-28 # i-7
lw t0,0(t0)
lw t1,0(t1)
lw t2,0(t2)
lw t3,0(t3)
sha256sig0 t0,t0
sha256sig1 t1,t1
add t0,t0,t1
add t0,t0,t2
add t0,t0,t3
la t1,w
sh2add t1,s0,t1
sw t0,0(t1)
addi s0,s0,1
li t0,64
blt s0,t0,1b

# Load initial working values
la t0,h
lw a0,0(t0)
lw a1,4(t0)
lw a2,8(t0)
lw a3,12(t0)
lw a4,16(t0)
lw a5,20(t0)
lw a6,24(t0)
lw a7,28(t0)

li s0,0
# Wikipedia calls this "Compression function main loop"
# S1
1: sha256sum1 t0,a4

# ch
and t1,a4,a5 # e AND f
andn t2,a6,a4 # g AND (NOT e) - also hey, turns out this instruction is actually useful for something
xor t1,t1,t2 # (e AND f) XOR (g AND (NOT e))

# temp1
add t0,t0,t1 # S1 + ch
add t0,t0,a7 # + h
la t1,k
sh2add t1,s0,t1
lw t1,0(t1)
add t0,t0,t1 # + k[i]
la t1,w
sh2add t1,s0,t1
lw t1,0(t1)
add t0,t0,t1 # + w[i]

# S0
sha256sum0 t1,a0

# maj
and t2,a0,a1 # a AND b
and t3,a0,a2 # a AND c
and t4,a1,a2 # b AND c
xor t2,t2,t3 # (a AND b) XOR (a AND c)
xor t2,t2,t4 # (a AND b) XOR (a AND c) XOR (b AND c)

# temp2
add t1,t1,t2 # S0 + maj

mv a7,a6 # h = g
mv a6,a5 # g = f
mv a5,a4 # f = e
add a4,a3,t0 # e = d + temp1
mv a3,a2 # d = c
mv a2,a1 # c = b
mv a1,a0 # b = a
add a0,t0,t1 # a = temp1 + temp2

addi s0,s0,1
li t0,64
blt s0,t0,1b

la t0,h
lw t1,0(t0)
add t1,t1,a0
sw t1,0(t0)
lw t1,4(t0)
add t1,t1,a1
sw t1,4(t0)
lw t1,8(t0)
add t1,t1,a2
sw t1,8(t0)
lw t1,12(t0)
add t1,t1,a3
sw t1,12(t0)
lw t1,16(t0)
add t1,t1,a4
sw t1,16(t0)
lw t1,20(t0)
add t1,t1,a5
sw t1,20(t0)
lw t1,24(t0)
add t1,t1,a6
sw t1,24(t0)
lw t1,28(t0)
add t1,t1,a7
sw t1,28(t0)

la a0,msghash
li a7,4
ecall # Print header line

la s0,h
la s1,h+32
1: lw a0,0(s0)
call hexdump
addi s0,s0,4
blt s0,s1,1b

li a7,10
ecall

hexdump:
mv t3,a0
li t0,8
li t1,0xf0000000
li t4,0x3a
1: and t2,t3,t1
srli t2,t2,28
addi t2,t2,0x30
blt t2,t4,2f
addi t2,t2,0x27
2: mv a0,t2
li a7,11
ecall
slli t3,t3,4
addi t0,t0,-1
bnez t0,1b
ret

h: .word 0x6a09e667,0xbb67ae85,0x3c6ef372,0xa54ff53a,0x510e527f,0x9b05688c,0x1f83d9ab,0x5be0cd19

k:
.word 0x428a2f98,0x71374491,0xb5c0fbcf,0xe9b5dba5,0x3956c25b,0x59f111f1,0x923f82a4,0xab1c5ed5
.word 0xd807aa98,0x12835b01,0x243185be,0x550c7dc3,0x72be5d74,0x80deb1fe,0x9bdc06a7,0xc19bf174
.word 0xe49b69c1,0xefbe4786,0x0fc19dc6,0x240ca1cc,0x2de92c6f,0x4a7484aa,0x5cb0a9dc,0x76f988da
.word 0x983e5152,0xa831c66d,0xb00327c8,0xbf597fc7,0xc6e00bf3,0xd5a79147,0x06ca6351,0x14292967
.word 0x27b70a85,0x2e1b2138,0x4d2c6dfc,0x53380d13,0x650a7354,0x766a0abb,0x81c2c92e,0x92722c85
.word 0xa2bfe8a1,0xa81a664b,0xc24b8b70,0xc76c51a3,0xd192e819,0xd6990624,0xf40e3585,0x106aa070
.word 0x19a4c116,0x1e376c08,0x2748774c,0x34b0bcb5,0x391c0cb3,0x4ed8aa4a,0x5b9cca4f,0x682e6ff3
.word 0x748f82ee,0x78a5636f,0x84c87814,0x8cc70208,0x90befffa,0xa4506ceb,0xbef9a3f7,0xc67178f2

w: .skip 64*4

message:
.word 0x68800000,0x00000000,0x00000000,0x00000000,0x00000000,0x00000000,0x00000000,0x00000000
.word 0x00000000,0x00000000,0x00000000,0x00000000,0x00000000,0x00000000,0x00000000,0x00000008

msgentermessage: .asciz "\nEnter message:\n> "
msgwait: .asciz "\n\nPlease wait..."
msghash: .asciz "\n\nSHA-256 hash:\n"