Parse non-scientific reals using exponents rather than factors

source/fortran/input.f90

@@ -4082,7 +4082,7 @@ subroutine string_to_real(string,length,rval,icode)
 
     !  Local variables
 
-    real(dp) :: valbdp,valadp,xfact
+    real(dp) :: valbdp,valadp,xexp
     integer :: iptr,izero,iexpon
     logical :: negatm,negate
 
@@ -4142,7 +4142,7 @@ subroutine string_to_real(string,length,rval,icode)
     ! *** Parse the mantissa - before the decimal point
 
     valbdp = 0.0D0
-    xfact = 0.1D0
+    xexp = -1.0D0
 20  continue
     if ((string(iptr:iptr) >= '0').and.(string(iptr:iptr) <= '9')) then
        valbdp = (valbdp * 10.0D0) + dble(ichar(string(iptr:iptr))-izero)
@@ -4163,8 +4163,8 @@ subroutine string_to_real(string,length,rval,icode)
     valadp = 0.0D0
 30  continue
     if ((string(iptr:iptr) >= '0').and.(string(iptr:iptr) <= '9')) then
-       valadp = valadp + (dble(ichar(string(iptr:iptr))-izero)*xfact)
-       xfact = xfact * 0.1D0
+       valadp = valadp + (dble(ichar(string(iptr:iptr))-izero)*(10.0D0 ** xexp))
+       xexp = xexp - 1.0D0
        iptr = iptr + 1
        if (iptr > length) goto 50
        goto 30

tests/unit/test_input.py

@@ -0,0 +1,60 @@
+import pytest
+from process import fortran
+
+
+def _create_input_file(directory, content: str):
+    file_location = directory / "IN.DAT"
+    with open(file_location, "w") as f:
+        f.write(content)
+
+    return str(file_location)
+
+
+@pytest.mark.parametrize(
+    ["epsvmc", "expected"],
+    [
+        (string, 1.0)
+        for string in [
+            "1.0",
+            "1.0D0",
+            "1.0d0",
+            "1.0e0",
+            "1.0E0",
+            "1.0D+0",
+            "1.0d+0",
+            "1.0e+0",
+            "1.0E+0",
+            "1.0D-0",
+            "1.0d-0",
+            "1.0e-0",
+            "1.0E-0",
+            "0.10D1",
+            "0.10d1",
+            "0.10E1",
+            "0.10e1",
+            "0.10D+1",
+            "0.10d+1",
+            "0.10E+1",
+            "0.10e+1",
+            "10.0D-1",
+            "10.0d-1",
+            "10.0E-1",
+            "10.0e-1",
+        ]
+    ]
+    + [
+        (string, 0.0080000000000000002)
+        for string in ["0.008", "8.0E-3", "8.0D-3", "8.0d-3", "8.0e-3"]
+    ],
+)
+def test_parse_real(epsvmc, expected, tmp_path):
+    """Tests the parsing of real numbers into PROCESS.
+
+    Program to get the expected value for 0.008 provided at https://github.com/ukaea/PROCESS/pull/3067
+    """
+    fortran.global_variables.fileprefix = _create_input_file(
+        tmp_path, f"epsvmc = {epsvmc}"
+    )
+    fortran.init_module.init()
+
+    assert fortran.numerics.epsvmc.item() == expected