fixes some issues with underscores in float literals. add more tests.

fixes some potential issues with underscores in float literals.
adds more checks for badly positionned underscores in float literals.
adds more test files.

lib/system/sysstr.nim

@@ -328,7 +328,7 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
     fraction: uint64
     frac_exponent= 0
     exp_sign = 1
-    first_digit = 0
+    first_digit = -1
     has_sign = false
 
   # Sign?
@@ -359,6 +359,7 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
   # Skip leading zero
   while s[i] == '0':
     inc(i)
+    while s[i] == '_': inc(i)
 
   if s[i] in {'0'..'9'}:
       first_digit = (s[i].ord - '0'.ord)
@@ -366,7 +367,7 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
   while s[i] in {'0'..'9'}:
     inc(kdigits)
     integer = integer * 10'u64 + (s[i].ord - '0'.ord).uint64
-    inc(i);
+    inc(i)
     while s[i] == '_': inc(i)
 
   # Fractional part?
@@ -374,11 +375,12 @@ proc nimParseBiggestFloat(s: string, number: var BiggestFloat,
     inc(i)
     # if no integer part, Skip leading zeros
     if kdigits <= 0:
-      while s[i] in {'_','0'}:
-        inc(i)
+      while s[i] == '0':
         inc(frac_exponent)
+        inc(i)
+        while s[i] == '_': inc(i)
 
-    if s[i] in {'0'..'9'}:
+    if first_digit == -1 and s[i] in {'0'..'9'}:
       first_digit = (s[i].ord - '0'.ord)
     # get fractional part
     while s[i] in {'0'..'9'}:

tests/float/tfloat6.nim

@@ -0,0 +1,21 @@
+discard """
+  file: "tfloat6.nim"
+  output: '''1e-06 : 1e-06
+1e-06 : 1e-06
+0.001 : 0.001
+1e-06 : 1e-06
+1e-06 : 1e-06
+10.000001 : 10.000001
+100.000001 : 100.000001'''
+"""
+
+import strutils
+
+echo "0.00_0001".parseFloat(), " : ", 1E-6
+echo "0.00__00_01".parseFloat(), " : ", 1E-6
+echo "0.0_01".parseFloat(), " : ", 0.001
+echo "0.00_000_1".parseFloat(), " : ", 1E-6
+echo "0.00000_1".parseFloat(), " : ", 1E-6
+
+echo "1_0.00_0001".parseFloat(), " : ", 10.000001
+echo "1__00.00_0001".parseFloat(), " : ", 1_00.000001

tests/float/tfloat7.nim

@@ -0,0 +1,26 @@
+discard """
+  file: "tfloat6.nim"
+  output: '''passed.
+passed.
+passed.
+passed.
+passed.
+passed.
+passed.'''
+"""
+
+import strutils
+template expect_fail(x: expr) =
+  try:
+    discard x
+    echo("expected to fail!")
+  except ValueError:
+    echo("passed.")
+
+expect_fail("1_0._00_0001".parseFloat())
+expect_fail("_1_0_00.0001".parseFloat())
+expect_fail("10.00.01".parseFloat())
+expect_fail("10.00E_01".parseFloat())
+expect_fail("10.00E_01".parseFloat())
+expect_fail("10.00E".parseFloat())
+expect_fail("10.00A".parseFloat())