Add support for negative integers in to_num_base inside stdlib_str2num (#1127)

* add: negative integer support for to_num and integer test cases

* add: more test case

* add: length check guard before sign check

* modify: do while loop

* clean implementation

* add early exit in case of empty strings

* move initialization of output value after comment line

Author: Mahmood-Sinan

src/strings/stdlib_str2num.fypp

@@ -128,13 +128,25 @@ module stdlib_str2num
         integer(int8), intent(out)  :: p !! position within the number
         integer(int8), intent(out)  :: stat !! status upon succes or failure to read
         ! -- Internal Variables
-        integer(int8)  :: val 
+        integer(int8)  :: val
+        integer(int8) :: sign
         !----------------------------------------------
         stat = 23 !! initialize error status with any number > 0
         !----------------------------------------------
         ! Find first non white space
         p = shift_to_nonwhitespace(s)
         !----------------------------------------------
+        ! Verify leading negative
+        sign = 1
+        if(p<=len(s)) then
+            if(iachar(s(p:p)) == minus_sign+digit_0 ) then
+                sign = -1
+                p = p + 1
+            end if
+        else
+            return
+        end if
+        !----------------------------------------------
         v = 0
         do while( p<=len(s) )
             val = iachar(s(p:p))-digit_0
@@ -145,9 +157,13 @@ module stdlib_str2num
                 exit
             end if
         end do
-        stat = 0
+        if(v >= 0) then
+            v = sign * v
+            stat = 0
+        else
+            stat = -1 !! Indicates integer overflow
+        end if
     end subroutine
-
     #:endfor
 
     elemental subroutine to_sp_base(s,v,p,stat)

test/string/test_string_to_number.fypp

@@ -1,6 +1,6 @@
 #: include "common.fypp"
 module test_string_to_number
-    use stdlib_kinds, only: sp, dp, xdp, qp
+    use stdlib_kinds, only: sp, dp, xdp, qp, int8, int16, int32, int64
     use stdlib_str2num, only: to_num
     use testdrive, only : new_unittest, unittest_type, error_type, check
     implicit none
@@ -21,6 +21,9 @@ contains
 #:if WITH_XDP
             , new_unittest("to_xdp", test_to_xdp) &
 #:endif
+#:for k1, t1 in INT_KINDS_TYPES
+            , new_unittest("to_${k1}$", test_to_${k1}$) &
+#:endfor
             ]
     end subroutine collect_string_to_number
 
@@ -132,6 +135,65 @@ contains
     end subroutine
 
     #:endfor
+
+    #:for k1, t1 in INT_KINDS_TYPES
+    subroutine test_to_${k1}$(error)
+        type(error_type), allocatable, intent(out) :: error
+        integer, parameter :: wp = ${k1}$
+        character(len=64) :: s
+
+        call check(error, ucheck("0"))
+        if (allocated(error)) return
+
+        call check(error, ucheck("-0"))
+        if (allocated(error)) return
+
+        call check(error, ucheck("123"))
+        if (allocated(error)) return
+
+        call check(error, ucheck("-123"))
+        if (allocated(error)) return
+
+        call check(error, ucheck("   99"))
+        if (allocated(error)) return
+
+        call check(error, ucheck("0005"))
+        if (allocated(error)) return
+
+        call check(error, ucheck("-0008"))
+        if (allocated(error)) return
+
+        call check(error, ucheck("78  "))
+        if (allocated(error)) return
+
+        call check(error, ucheck("   -42   "))
+        if (allocated(error)) return
+
+        write(s,'(i0)') huge(0_wp)
+        call check(error, ucheck(trim(s)))
+        if (allocated(error)) return
+
+        write(s,'(i0)') -huge(0_wp)-1
+        call check(error, ucheck(trim(s)))
+        if (allocated(error)) return
+
+    contains
+        logical function ucheck(s)
+            character(*), intent(in) :: s
+            integer(${k1}$) :: formatted_read_out
+            integer(${k1}$) :: to_num_out
+
+            ucheck = .true.
+            read(s,*) formatted_read_out
+            to_num_out = to_num(s, to_num_out)
+            if(to_num_out /= formatted_read_out) then
+                write(*,"('formatted read : ', i0)") formatted_read_out
+                write(*,"('to_num         : ', i0)") to_num_out
+                ucheck = .false.
+            end if
+        end function
+    end subroutine
+    #:endfor
 
 end module test_string_to_number