Add routines for saving arrays in npy format

src/CMakeLists.txt

@@ -7,6 +7,7 @@ set(fppFiles
     stdlib_bitsets_64.fypp
     stdlib_bitsets_large.fypp
     stdlib_io.fypp
+    stdlib_io_npy.fypp
     stdlib_kinds.fypp
     stdlib_linalg.fypp
     stdlib_linalg_diag.fypp

src/Makefile.manual

@@ -4,6 +4,7 @@ SRCFYPP = \
         stdlib_bitsets_large.fypp \
         stdlib_bitsets.fypp \
         stdlib_io.fypp \
+        stdlib_io_npy.fypp \
         stdlib_kinds.fypp \
         stdlib_linalg.fypp \
         stdlib_linalg_diag.fypp \

src/stdlib_io_npy.fypp

@@ -0,0 +1,219 @@
+! SPDX-Identifer: MIT
+
+#:include "common.fypp"
+#:set RANKS = range(1, MAXRANK + 1)
+#:set KINDS_TYPES = REAL_KINDS_TYPES + INT_KINDS_TYPES + CMPLX_KINDS_TYPES
+
+!> Description of the npy format taken from
+!> https://numpy.org/doc/stable/reference/generated/numpy.lib.format.html
+!>
+!>## Format Version 1.0
+!>
+!> The first 6 bytes are a magic string: exactly \x93NUMPY.
+!>
+!> The next 1 byte is an unsigned byte:
+!> the major version number of the file format, e.g. \x01.
+!>
+!> The next 1 byte is an unsigned byte:
+!> the minor version number of the file format, e.g. \x00.
+!> Note: the version of the file format is not tied to the version of the numpy package.
+!>
+!> The next 2 bytes form a little-endian unsigned short int:
+!> the length of the header data HEADER_LEN.
+!>
+!> The next HEADER_LEN bytes form the header data describing the array’s format.
+!> It is an ASCII string which contains a Python literal expression of a dictionary.
+!> It is terminated by a newline (\n) and padded with spaces (\x20) to make the total
+!> of len(magic string) + 2 + len(length) + HEADER_LEN be evenly divisible by 64 for
+!> alignment purposes.
+!>
+!> The dictionary contains three keys:
+!>
+!> - “descr”: dtype.descr
+!>   An object that can be passed as an argument to the numpy.dtype constructor
+!>   to create the array’s dtype.
+!>
+!> - “fortran_order”: bool
+!>   Whether the array data is Fortran-contiguous or not. Since Fortran-contiguous
+!>   arrays are a common form of non-C-contiguity, we allow them to be written directly
+!>   to disk for efficiency.
+!>
+!> - “shape”: tuple of int
+!>   The shape of the array.
+!>
+!> For repeatability and readability, the dictionary keys are sorted in alphabetic order.
+!> This is for convenience only. A writer SHOULD implement this if possible. A reader MUST
+!> NOT depend on this.
+!>
+!> Following the header comes the array data. If the dtype contains Python objects
+!> (i.e. dtype.hasobject is True), then the data is a Python pickle of the array.
+!> Otherwise the data is the contiguous (either C- or Fortran-, depending on fortran_order)
+!> bytes of the array. Consumers can figure out the number of bytes by multiplying the
+!> number of elements given by the shape (noting that shape=() means there is 1 element)
+!> by dtype.itemsize.
+!>
+!>## Format Version 2.0
+!>
+!> The version 1.0 format only allowed the array header to have a total size of 65535 bytes.
+!> This can be exceeded by structured arrays with a large number of columns.
+!> The version 2.0 format extends the header size to 4 GiB. numpy.save will automatically
+!> save in 2.0 format if the data requires it, else it will always use the more compatible
+!> 1.0 format.
+!>
+!> The description of the fourth element of the header therefore has become:
+!> “The next 4 bytes form a little-endian unsigned int: the length of the header data
+!> HEADER_LEN.”
+!>
+!>## Format Version 3.0
+!>
+!> This version replaces the ASCII string (which in practice was latin1) with a
+!> utf8-encoded string, so supports structured types with any unicode field names.
+module stdlib_io_npy
+    use stdlib_error, only : error_stop
+    use stdlib_kinds, only : int8, int16, int32, int64, sp, dp, xdp, qp
+    use stdlib_strings, only : to_string
+    implicit none
+    private
+
+    public :: save_npy
+
+
+    !> Save multidimensional array in npy format
+    interface save_npy
+    #:for k1, t1 in KINDS_TYPES
+      #:for rank in RANKS
+        module procedure save_npy_${t1[0]}$${k1}$_${rank}$
+      #:endfor
+    #:endfor
+    end interface save_npy
+
+
+    character(len=*), parameter :: nl = char(10)
+
+    character(len=*), parameter :: &
+        type_iint8 = "<i1", type_iint16 = "<i2", type_iint32 = "<i4", type_iint64 = "<i8", &
+        type_rsp = "<f4", type_rdp = "<f8", type_rxdp = "<f10", type_rqp = "<f16", &
+        type_csp = "<c8", type_cdp = "<c16", type_cxdp = "<c20", type_cqp = "<c32"
+
+    character(len=*), parameter :: &
+        & magic_number = char(int(z"93")), &
+        & magic_string = "NUMPY"
+
+contains
+
+
+    !> Generate magic header string for npy format
+    pure function magic_header(major, minor) result(str)
+        !> Major version of npy format
+        integer, intent(in) :: major
+        !> Minor version of npy format
+        integer, intent(in) :: minor
+        !> Magic string for npy format
+        character(len=8) :: str
+
+        str = magic_number // magic_string // char(major) // char(minor)
+    end function magic_header
+
+
+    !> Generate header for npy format
+    pure function npy_header(vtype, vshape) result(str)
+        !> Type of variable
+        character(len=*), intent(in) :: vtype
+        !> Shape of variable
+        integer, intent(in) :: vshape(:)
+        !> Header string for npy format
+        character(len=:), allocatable :: str
+
+        integer, parameter :: len_v10 = 8 + 2, len_v20 = 8 + 4
+
+        str = &
+            "{'descr': '"//vtype//&
+            "', 'fortran_order': True, 'shape': "//&
+            shape_str(vshape)//", }"
+
+        if (len(str) + len_v10 >= 65535) then
+            str = str // &
+                & repeat(" ", 16 - mod(len(str) + len_v20 + 1, 16)) // nl
+            str = magic_header(2, 0) // to_bytes_i4(int(len(str))) // str
+        else
+            str = str // &
+                & repeat(" ", 16 - mod(len(str) + len_v10 + 1, 16)) // nl
+            str = magic_header(1, 0) // to_bytes_i2(int(len(str))) // str
+        end if
+    end function npy_header
+
+    !> Write integer as byte string in little endian encoding
+    pure function to_bytes_i4(val) result(str)
+        !> Integer value to convert to bytes
+        integer, intent(in) :: val
+        !> String of bytes
+        character(len=4), allocatable :: str
+
+        str = char(mod(val, 2**8)) // &
+            & char(mod(val, 2**16) / 2**8) // &
+            & char(mod(val, 2**32) / 2**16) // &
+            & char(val / 2**32)
+    end function to_bytes_i4
+
+
+    !> Write integer as byte string in little endian encoding, 2-byte truncated version
+    pure function to_bytes_i2(val) result(str)
+        !> Integer value to convert to bytes
+        integer, intent(in) :: val
+        !> String of bytes
+        character(len=2), allocatable :: str
+
+        str = char(mod(val, 2**8)) // &
+            & char(mod(val, 2**16) / 2**8)
+    end function to_bytes_i2
+
+
+    !> Print array shape as tuple of int
+    pure function shape_str(vshape) result(str)
+        !> Shape of variable
+        integer, intent(in) :: vshape(:)
+        !> Shape string for npy format
+        character(len=:), allocatable :: str
+
+        integer :: i
+
+        str = "("
+        do i = 1, size(vshape)
+            str = str//to_string(vshape(i))//", "
+        enddo
+        str = str//")"
+    end function shape_str
+
+
+#:for k1, t1 in KINDS_TYPES
+  #:for rank in RANKS
+    !> Save ${rank}$-dimensional array in npy format
+    subroutine save_npy_${t1[0]}$${k1}$_${rank}$(filename, array, iostat)
+        character(len=*), intent(in) :: filename
+        ${t1}$, intent(in) :: array${ranksuffix(rank)}$
+        integer, intent(out), optional :: iostat
+        character(len=*), parameter :: vtype = type_${t1[0]}$${k1}$
+
+        integer :: io, stat
+
+        open(newunit=io, file=filename, form="unformatted", access="stream", iostat=stat)
+        if (stat == 0) then
+            write(io, iostat=stat) npy_header(vtype, shape(array))
+        end if
+        if (stat == 0) then
+            write(io, iostat=stat) array
+        end if
+        close(io, iostat=stat)
+
+        if (present(iostat)) then
+            iostat = stat
+        else if (stat /= 0) then
+            call error_stop("Failed to write array to file '"//filename//"'")
+        end if
+
+    end subroutine save_npy_${t1[0]}$${k1}$_${rank}$
+  #:endfor
+#:endfor
+
+
+end module stdlib_io_npy