git.zerfleddert.de Git - rsbs2/blob - rsb-crc.c

   1 #define POLY 0x04c11db7
   2
   3 /* Theory of operation:
   4  * (arm-elf-objdump -b binary -m arm -M reg-names-raw -D RSB_S2_SINGLE.bin)
   5  *
   6  * 440: push  {r4, r5, r6, r7, r8, r9, r10, r11, r14}
   7  * 444: mov   r11, r0
   8  * 448: mov   r10, r1
   9  * 44c: mov   r14, r2
  10  * 450: mov   r6, #0    ; 0x0
  11  * 454: b     0x4a0
  12  * 458: add   r3, r6, r10
  13  * 45c: ldrb  r3, [r3]
  14  * 460: lsl   r3, r3, #24
  15  * 464: eor   r11, r11, r3
  16  * 468: mov   r5, #8    ; 0x8
  17  * 46c: and   r3, r11, #-2147483648     ; 0x80000000
  18  * 470: cmp   r3, #0    ; 0x0
  19  * 474: beq   0x48c
  20  * 478: lsl   r3, r11, #1
  21  * 47c: ldr   r12, [pc, #64]    ; 0x4c4
  22  * 480: eor   r0, r3, r12
  23  * 484: mov   r11, r0
  24  * 488: b     0x490
  25  * 48c: lsl   r11, r11, #1
  26  * 490: sub   r5, r5, #1        ; 0x1
  27  * 494: cmp   r5, #0            ; 0x0
  28  * 498: bne   0x46c
  29  * 49c: add   r6, r6, #1        ; 0x1
  30  * 4a0: cmp   r6, r14
  31  * 4a4: blt   0x458
  32  * 4a8: mov   r0, r11
  33  * 4ac: pop   {r4, r5, r6, r7, r8, r9, r10, r11, r15}
  34  * 4c4: DATA: 0x04c11db7
  35  */
  36
  37 unsigned int rsb_crc(unsigned int r11_crc, unsigned char *r10_buf, unsigned int r14_len) {
  38         unsigned int r6_pos = 0;
  39         unsigned int r3_data;
  40         int r5_bit;
  41
  42         while (r6_pos < r14_len) {
  43                 r3_data = (*(r6_pos+r10_buf)) << 24;
  44                 r11_crc = r11_crc ^ r3_data;
  45
  46                 r5_bit = 8;
  47
  48                 do {
  49                         r3_data = r11_crc & 0x80000000;
  50
  51                         if (r3_data != 0) {
  52                                 r3_data = r11_crc << 1;
  53                                 r11_crc = r3_data ^ POLY;
  54                         } else {
  55                                 r11_crc = r11_crc << 1;
  56                         }
  57                         r5_bit--;
  58                 } while (r5_bit);
  59
  60                 r6_pos++;
  61         }
  62
  63         return r11_crc;
  64 }