Convert a 32 bit binary IPv4 address to its quad-dotted notation

x86-16 machine code, IBM PC DOS, 54 47 45 bytes

Binary:

00000000: be82 00b3 04b1 08ac d0d8 d0d4 e2f9 8ac4  ................
00000010: 41d4 0a50 8ac4 84c0 75f6 580c 30b4 0ecd  A..P....u.X.0...
00000020: 10e2 f74b 7406 b02e cd10 ebd9 c3         ...Kt........

Build and test BIN2IP.COM using xxd -r from above.

Unassembled listing:

BE 0082     MOV  SI, 82H        ; command line input address
B3 04       MOV  BL, 4          ; loop 4 bytes 
        BYTE_LOOP:
B1 08       MOV  CL, 8          ; loop 8 bits 
        BIT_LOOP: 
AC          LODSB               ; load next bit char into AL 
D0 D8       RCR  AL, 1          ; put LSB of char into CF 
D0 D4       RCL  AH, 1          ; put CF into LSB of byte value, then shift left
E2 F9       LOOP BIT_LOOP       ; continue bit loop 
8A C4       MOV  AL, AH         ; put byte result into AL
        GET_DIGIT: 
D4 0A       AAM                 ; byte divide by 10, AH = AL / 10, AL = AL % 10 
50          PUSH AX             ; save remainder in AL on stack 
8A C4       MOV  AL, AH         ; put quotient back into AL 
41          INC  CX             ; increment decimal digit count 
D4 C0       TEST AL, AL         ; quotient = 0? 
75 F6       JNZ  GET_DIGIT      ; if not, continue looping 
        PRINT_DIGIT: 
58          POP  AX             ; restore digit in AL 
0C 30       OR   AL, '0'        ; ASCII convert              
B4 0E       MOV  AH, 0EH        ; BIOS write char function   
CD 10       INT  10H            ; write to console 
E2 F7       LOOP PRINT_DIGIT    ; loop until done 
4B          DEC  BX             ; is last byte? 
74 06       JZ   END_LOOP       ; if so, don't display a '.' 
B0 2E       MOV  AL, '.'        ; otherwise display '.'
CD 10       INT  10H            ; write to console 
        END_LOOP:
75 D7       JNZ  BYTE_LOOP      ; continue byte loop 
C3          RET                 ; exit to DOS 

Output:

A standalone PC DOS executable. Input is command line, output to console.

Notes:

The "interesting part" (converting binary string to bytes) is about 15 bytes, whereas the rest of code is writing the itoa() function to convert binary bytes into a decimal string representation for display.

• -2 bytes eliminating unnecessary PUSH/POP thx to @PeterCordes!

05AB1E, 6 bytes

4äC'.ý

Try it online or verify all test cases.

Explanation:

4ä       # Convert the (implicit) input-string into 4 equal-sized parts
  C      # Convert each part from binary to an integer
   '.ý  '# Join this list by "."
         # (after which the result is output implicitly)

C (gcc), 48 bytes

i;f(n){for(i=4;i--;)printf(".%hhu"+i/3,n>>i*8);}

Takes as input a 32-bit integer.

Thanks to ceilingcat and gastropner for getting this answer where it is now!

Try it online!