+/*
+ * void serpent_init(const void* key, uint16_t keysize_b, serpent_ctx_t* ctx)
+ */
+/*
+ * param key is passed in r24:r25
+ * param keysize is passed in r22:r23
+ * param ctx is passed in r20:r21
+ */
+.global serpent_init
+serpent_init:
+ stack_alloc 32
+ adiw r30, 1
+ push_ r30, r31
+ movw r26, r22
+ adiw r26, 7
+ tst r27
+ breq 1f
+ ldi r26, 32
+ rjmp 2f
+1:
+ lsr r26
+ lsr r26
+ lsr r26
+2:
+ mov r22, r26
+ bst r22, 5 /* store in T if we have to do the "append 1 thing"*/
+ ldi r27, 32
+3: /* set buffer to zero */
+ st Z+, r1
+ dec r27
+ brne 3b
+
+ movw r26, r24 /* X points to the key */
+ sbiw r30, 32
+ tst r22
+ breq 5f /* if keylength_b==0 */
+4: /* copy keybytes to buffer */
+ ld r19, X+
+ st Z+, r19
+ dec r22
+ brne 4b
+5:
+ brts 7f /* if keylength_b == 256 */
+ ldi r18, 0x01
+ andi r22, 0x07
+ brne 6f
+ st Z, r18
+ rjmp 7f
+6: /* shift the one to the right position */
+ lsl r18
+ dec r22
+ brne 6b
+ or r18, r19
+ st -Z, r18
+7: /* post "appending 1 thing" buffer is ready for subkey generation */
+ movw r26, r20 /* X points to the context */
+
+ pop_ r19, r18 /* r18:r19 points to the buffer */
+ push r16
+ clr r16
+8:
+ movw r24, r18
+ mov r22, r16
+ rcall serpent_gen_w
+ movw r30, r18
+ ldi r20, 7*4
+1: /* the memmove */
+ ldd r0, Z+4
+ st Z+, r0
+ dec r20
+ brne 1b
+ /* store new word in buffer and context */
+ st Z+, r22
+ st Z+, r23
+ st Z+, r24
+ st Z+, r25
+ st X+, r22
+ st X+, r23
+ st X+, r24
+ st X+, r25
+
+ inc r16
+ cpi r16, 132
+ brne 8b
+
+ push_ r28, r29
+ movw r28, r26
+ subi r28, lo8(132*4)
+ sbci r29, hi8(132*4)
+ ldi r16, 33
+2:
+ movw r24, r28
+ adiw r28, 16
+ ldi r22, 2
+ add r22, r16
+ rcall sbox128
+ dec r16
+ brne 2b
+ pop_ r29, r28, r16
+ stack_free 32
+ ret
+
+/*
+ * void serpent_enc(void* buffer, const serpent_ctx_t* ctx){
+ */
+/*
+ * param buffer is passed in r24:r25
+ * param ctx is passed in r22:r23
+ */
+.global serpent_enc
+serpent_enc:
+
+ push_ r12, r13, r14, r15, r16
+ clr r16
+ movw r14, r24
+ movw r12, r22
+1:
+ movw r24, r14
+ movw r22, r12
+ ldi r20, 16
+ add r12, r20
+ adc r13, r1
+ clr r21
+ rcall memxor
+ movw r24, r14
+ mov r22, r16
+ rcall sbox128
+ movw r24, r14
+ rcall serpent_lt
+
+ inc r16
+ cpi r16, 31
+ brne 1b
+
+ movw r24, r14
+ movw r22, r12
+ ldi r20, 16
+ add r12, r20
+ adc r13, r1
+ clr r21
+ rcall memxor
+ movw r24, r14
+ mov r22, r16
+ rcall sbox128
+
+ inc r16
+ movw r24, r14
+ movw r22, r12
+ ldi r20, 16
+ clr r21
+ pop_ r16, r15, r14, r13, r12
+ rjmp memxor
+
+/*
+ * void serpent_dec(void* buffer, const serpent_ctx_t* ctx){
+ */
+/*
+ * param buffer is passed in r24:r25
+ * param ctx is passed in r22:r23
+ */
+.global serpent_dec
+serpent_dec:
+ push_ r12, r13, r14, r15, r16
+ movw r14, r24
+// ldi r16, lo8(32*16)
+// add r22, r16
+ ldi r16, hi8(32*16)
+ add r23, r16
+ movw r12, r22
+ ldi r20, 16
+ clr r21
+ rcall memxor
+
+ movw r24, r14
+ ldi r22, 31
+ call inv_sbox128
+
+ movw r24, r14
+ ldi r20, 16
+ sub r12, r20
+ sbc r13, r1
+ movw r22, r12
+ clr r21
+ rcall memxor
+ ldi r16, 31
+1:
+ dec r16
+ movw r24, r14
+ rcall serpent_inv_lt
+ movw r24, r14
+ mov r22, r16
+ rcall inv_sbox128
+ movw r24, r14
+ ldi r20, 16
+ sub r12, r20
+ sbc r13, r1
+ movw r22, r12
+ clr r21
+ rcall memxor
+
+ tst r16
+ brne 1b
+ pop_ r16, r15, r14, r13, r12
+ ret
+
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