decode_bits Subroutine

  1. befor64.F90
  2. befor64
  3. decode_bits

private pure subroutine decode_bits(code, bits)

Arguments

Type IntentOptional AttributesName
character(len=*), intent(in) :: code

Characters code.
integer(kind=I1P), intent(out) :: bits(1:)

Bits decoded.

Description

Decode a base64 string into a sequence of bits stream.

The base64 string must be parsed with a strike of 4 characters and converted into a 3 bytes stream. Considering the base64 code QUJD the decoding process must do

 +-b64 char--+-b64 char--+-b64 char--+-b64 char--+
 |      Q    |      U    |      J    |      D    |
 +-b64 index-+-b64 index-+-b64 index-+-b64 index-+
 !      16   |      20   |      9    |      3    |
 +-6 bits----+-6 bits----+-6 bits----+-6 bits----+
 |0 1 0 0 0 0|0 1 0 1 0 0|0 0 1 0 0 1|0 0 0 0 1 1|
 +-----------+---+-------+-------+---+-----------+
 |0 1 0 0 0 0 0 1|0 1 0 0 0 0 1 0|0 1 0 0 0 0 1 1|
 +-----8 bits----+-----8 bits----+-----8 bits----+

Called By

proc~~decode_bits~~CalledByGraph proc~decode_bits decode_bits proc~b64_decode_r16 b64_decode_R16 proc~b64_decode_r16->proc~decode_bits proc~b64_decode_i2 b64_decode_I2 proc~b64_decode_i2->proc~decode_bits proc~b64_decode_string b64_decode_string proc~b64_decode_string->proc~decode_bits proc~b64_decode_i1_a b64_decode_I1_a proc~b64_decode_i1_a->proc~decode_bits proc~b64_decode_i4 b64_decode_I4 proc~b64_decode_i4->proc~decode_bits proc~b64_decode_i4_a b64_decode_I4_a proc~b64_decode_i4_a->proc~decode_bits proc~b64_decode_r16_a b64_decode_R16_a proc~b64_decode_r16_a->proc~decode_bits proc~b64_decode_i8 b64_decode_I8 proc~b64_decode_i8->proc~decode_bits proc~b64_decode_string_a b64_decode_string_a proc~b64_decode_string_a->proc~decode_bits proc~b64_decode_i8_a b64_decode_I8_a proc~b64_decode_i8_a->proc~decode_bits proc~b64_decode_r4 b64_decode_R4 proc~b64_decode_r4->proc~decode_bits proc~b64_decode_r4_a b64_decode_R4_a proc~b64_decode_r4_a->proc~decode_bits proc~b64_decode_r8 b64_decode_R8 proc~b64_decode_r8->proc~decode_bits proc~b64_decode_i1 b64_decode_I1 proc~b64_decode_i1->proc~decode_bits proc~b64_decode_r8_a b64_decode_R8_a proc~b64_decode_r8_a->proc~decode_bits proc~b64_decode_i2_a b64_decode_I2_a proc~b64_decode_i2_a->proc~decode_bits proc~b64_decode_up b64_decode_up proc~b64_decode_up->proc~b64_decode_i2 proc~b64_decode_up->proc~b64_decode_string proc~b64_decode_up->proc~b64_decode_i4 proc~b64_decode_up->proc~b64_decode_i8 proc~b64_decode_up->proc~b64_decode_r4 proc~b64_decode_up->proc~b64_decode_r8 proc~b64_decode_up->proc~b64_decode_i1 interface~b64_decode b64_decode interface~b64_decode->proc~b64_decode_i2 interface~b64_decode->proc~b64_decode_string interface~b64_decode->proc~b64_decode_i1_a interface~b64_decode->proc~b64_decode_i4 interface~b64_decode->proc~b64_decode_i4_a interface~b64_decode->proc~b64_decode_i8 interface~b64_decode->proc~b64_decode_string_a interface~b64_decode->proc~b64_decode_i8_a interface~b64_decode->proc~b64_decode_r4 interface~b64_decode->proc~b64_decode_r4_a interface~b64_decode->proc~b64_decode_r8 interface~b64_decode->proc~b64_decode_i1 interface~b64_decode->proc~b64_decode_r8_a interface~b64_decode->proc~b64_decode_i2_a proc~decode decode proc~decode->interface~b64_decode proc~autotest autotest proc~autotest->interface~b64_decode proc~b64_decode_up_a b64_decode_up_a proc~b64_decode_up_a->proc~b64_decode_i1_a proc~b64_decode_up_a->proc~b64_decode_i4_a proc~b64_decode_up_a->proc~b64_decode_string_a proc~b64_decode_up_a->proc~b64_decode_i8_a proc~b64_decode_up_a->proc~b64_decode_r4_a proc~b64_decode_up_a->proc~b64_decode_r8_a proc~b64_decode_up_a->proc~b64_decode_i2_a interface~b64_decode_up b64_decode_up interface~b64_decode_up->proc~b64_decode_up_a interface~b64_decode_up->proc~b64_decode_up_a interface~b64_decode_up->interface~b64_decode_up
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Variables

TypeVisibility AttributesNameInitial
integer(kind=I1P), public :: sixb(1:4)

6 bits slices (stored into 8 bits integer) of 24 bits input.
integer(kind=I8P), public :: c

Counter.
integer(kind=I8P), public :: e

Counter.
integer(kind=I8P), public :: Nb

Length of bits array.

Source Code

  pure subroutine decode_bits(code, bits)
  !---------------------------------------------------------------------------------------------------------------------------------
  !< Decode a base64 string into a sequence of bits stream.
  !<
  !< The base64 string must be parsed with a strike of 4 characters and converted into a 3 bytes stream. Considering the base64 code
  !< `QUJD` the decoding process must do
  !<```
  !< +-b64 char--+-b64 char--+-b64 char--+-b64 char--+
  !< |      Q    |      U    |      J    |      D    |
  !< +-b64 index-+-b64 index-+-b64 index-+-b64 index-+
  !< !      16   |      20   |      9    |      3    |
  !< +-6 bits----+-6 bits----+-6 bits----+-6 bits----+
  !< |0 1 0 0 0 0|0 1 0 1 0 0|0 0 1 0 0 1|0 0 0 0 1 1|
  !< +-----------+---+-------+-------+---+-----------+
  !< |0 1 0 0 0 0 0 1|0 1 0 0 0 0 1 0|0 1 0 0 0 0 1 1|
  !< +-----8 bits----+-----8 bits----+-----8 bits----+
  !<```
  !< @note The bits pattern is returned as a 1-byte element array, the dimension of witch must be computed outside this procedure.
  !<
  !< @warning This procedure is the backend of decoding, thus it must be never called outside the module.
  !---------------------------------------------------------------------------------------------------------------------------------
  character(*), intent(in)  :: code      !< Characters code.
  integer(I1P), intent(out) :: bits(1:)  !< Bits decoded.
  integer(I1P)              :: sixb(1:4) !< 6 bits slices (stored into 8 bits integer) of 24 bits input.
  integer(I8P)              :: c         !< Counter.
  integer(I8P)              :: e         !< Counter.
  integer(I8P)              :: Nb        !< Length of bits array.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  Nb=size(bits,dim=1,kind=I8P)
  e = 1_I8P
  do c=1_I8P,len(code),4_I8P ! loop over code characters: 3 bytes (24 bits) scanning
    sixb = 0_I1P
    sixb(1) = index(base64,code(c  :c  )) - 1
    sixb(2) = index(base64,code(c+1:c+1)) - 1
    sixb(3) = index(base64,code(c+2:c+2)) - 1
    sixb(4) = index(base64,code(c+3:c+3)) - 1
      call mvbits(sixb(1),0,6,bits(e  ),2) ; call mvbits(sixb(2),4,2,bits(e  ),0)
    if (e+1<=Nb) then
      call mvbits(sixb(2),0,4,bits(e+1),4) ; call mvbits(sixb(3),2,4,bits(e+1),0)
    endif
    if (e+2<=Nb) then
      call mvbits(sixb(3),0,2,bits(e+2),6) ; call mvbits(sixb(4),0,6,bits(e+2),0)
    endif
    e = e + 3_I8P
  enddo
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endsubroutine decode_bits