Proposal for a reference string to number conversion facility in stdlib

ci/fpm-deployment.sh

@@ -9,7 +9,8 @@ destdir="${DESTDIR:-stdlib-fpm}"
 fypp="${FYPP:-$(which fypp)}"
 
 # Arguments for the fypp preprocessor
-fyflags="${FYFLAGS:--DMAXRANK=4}"
+maxrank=4
+fyflags="${FYFLAGS:--DMAXRANK=$maxrank}"
 
 # Number of parallel jobs for preprocessing
 if [ $(uname) = "Darwin" ]; then
@@ -44,6 +45,12 @@ mkdir -p "$destdir/src" "$destdir/test" "$destdir/example"
 find src -maxdepth 1 -iname "*.fypp" \
   | cut -f1 -d. | xargs -P "$njob" -I{} "$fypp" "{}.fypp" "$destdir/{}.f90" $fyflags
 
+find test -name "test_*.fypp" -exec cp {} "$destdir/test/" \;
+fyflags="${fyflags} -I src"
+find $destdir/test -maxdepth 1 -iname "*.fypp" \
+  | cut -f1 -d. | xargs -P "$njob" -I{} "$fypp" "{}.fypp" "{}.f90" $fyflags
+find $destdir/test -name "test_*.fypp" -exec rm {} \;
+
 # Collect stdlib source files
 find src -maxdepth 1 -iname "*.f90" -exec cp {} "$destdir/src/" \;
 find test -name "test_*.f90" -exec cp {} "$destdir/test/" \;

doc/specs/stdlib_str2num.md

@@ -0,0 +1,82 @@
+---
+title: str2num
+---
+
+# The `stdlib_str2num` module
+
+This module proposes a function-style interface for string-to-number conversion. It also profits from Fortran's interfaces to implement precision-dependant algorithms to maximize runtime efficiency.
+
+[TOC]
+
+## `to_num` - conversion of strings to numbers
+
+### Status
+
+Experimental
+
+### Description
+
+Convert a string or an array of strings to numerical types.
+
+### Syntax
+
+`number = [[stdlib_str2num(module):to_num(interface)]](string, mold)`
+
+### Arguments
+
+`string`: argument has `intent(in)` and is of type `character(*)`.
+
+`mold`: argument has `intent(in)` and is of numerical type (that is of `integer` or of `real`). **Note**: The type of the `mold` argument defines the type of the result.
+
+### Return value
+
+Return a scalar of numerical type (i.e., `integer`, or `real`).
+
+### Example
+
+```fortran
+{!example/strings/example_string_to_number.f90!}
+```
+
+## `to_num_from_stream` - conversion of a stream of values in a string to numbers
+
+### Status
+
+Experimental
+
+### Description
+
+Convert a stream of values in a string to an array of values.
+
+### Syntax
+
+`number = [[stdlib_str2num(module):to_num_from_stream(interface)]](string, mold)`
+
+### Arguments
+
+`string`: argument has `intent(in)` and is of type `character(:), pointer`.
+
+`mold`: argument has `intent(in)` and is of numerical type (currently of `integer` or `real`). **Note**: The type of the `mold` argument defines the type of the result.
+
+### Return value
+
+Return a scalar of numerical type (i.e., `integer` or `real`).
+
+### Example
+
+```fortran
+{!example/strings/example_stream_of_strings_to_numbers.f90!}
+```
+
+## Note
+The accuracy of the conversion is implementation dependent; it is recommended that implementers guarantee precision down to the last 3 bits.
+
+**The current implementation has been tested to provide for** :
+
+`sp`  : exact match
+
+`dp`  : precision up-to epsilon(0.0_dp)
+
+`qp` : precision around 200*epsilon(0.0_qp)
+
+Where precision refers to the relative difference between `to_num` and `read`. On the other hand, `to_num` provides speed-ups ranging from 4x to >10x compared to the intrinsic `read`.

example/strings/CMakeLists.txt

@@ -10,3 +10,5 @@ ADD_EXAMPLE(starts_with)
 ADD_EXAMPLE(strip)
 ADD_EXAMPLE(to_string)
 ADD_EXAMPLE(zfill)
+ADD_EXAMPLE(string_to_number)
+ADD_EXAMPLE(stream_of_strings_to_numbers)

example/strings/example_stream_of_strings_to_numbers.f90

@@ -0,0 +1,22 @@
+program example_stream_of_strings_to_numbers
+    use stdlib_kinds, only: dp
+    use stdlib_str2num, only: to_num_from_stream
+    character(:), allocatable, target :: chain
+    character(len=:), pointer :: cptr
+    real(dp), allocatable :: r(:), p(:)
+    integer :: i 
+
+    chain = " 1.234   1.E1 1e0     0.1234E0  12.21e+001 -34.5E1"
+    allocate( r(6), p(6) )
+    !> Example for streamline conversion using `to_num_from_stream`
+    cptr => chain
+    do i =1, 6
+        r(i) = to_num_from_stream( cptr , r(i) ) !> the pointer is shifted within the function
+    end do
+    read(chain,*) p
+    print *, "Reading with to_num_from_stream"
+    print *, r
+    print *, "Reading with formatted read"
+    print *, p
+
+end program example_stream_of_strings_to_numbers

example/strings/example_string_to_number.f90

@@ -0,0 +1,10 @@
+program example_string_to_number
+    use stdlib_kinds, only: dp
+    use stdlib_str2num, only: to_num
+    implicit none
+    character(:), allocatable :: txt
+    real(dp) :: x
+
+    txt = ' 8.8541878128e−12 '
+    x = to_num( txt , x )
+  end program example_string_to_number

src/CMakeLists.txt

@@ -55,6 +55,7 @@ set(fppFiles
     stdlib_math_is_close.fypp
     stdlib_math_all_close.fypp
     stdlib_math_diff.fypp
+    stdlib_str2num.fypp
     stdlib_string_type.fypp
     stdlib_string_type_constructor.fypp
     stdlib_strings_to_string.fypp