Merge pull request #506 from toml-lang/signed-zeros-and-non-finite-fl…

…oats

Add special float values and clarify signed zeros

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## HEAD
 
+* Add special float values (inf, nan)
 * Rename Datetime to Offset Date-Time.
 * Add Local Date-Time.
 * Add Local Date.
@@ -19,6 +20,7 @@
 * Clarify that literal strings can be table keys.
 * Clarify that at least millisecond precision expected for Date-Time and Time.
 * Clarify that comments are OK in multiline arrays.
+* Clarify that +0, -0, +0.0, and -0.0 are valid and what they mean.
 * TOML has a logo!
 
 ## 0.4.0 / 2015-02-12

README.md

@@ -296,16 +296,17 @@ int6 = 5_349_221
 int7 = 1_2_3_4_5     # VALID but discouraged
 ```
 
-Leading zeros are not allowed. Hex, octal, and binary forms are not allowed.
-Values such as "infinity" and "not a number" that cannot be expressed as a
-series of digits are not allowed.
+Leading zeros are not allowed. Integer values `-0` and `+0` are valid and
+identical to an unprefixed zero. Hex, octal, and binary forms are not allowed.
 
 64 bit (signed long) range expected (−9,223,372,036,854,775,808 to
 9,223,372,036,854,775,807).
 
 Float
 -----
 
+Floats should be implemented as IEEE 754 binary64 values.
+
 A float consists of an integer part (which follows the same rules as integer
 values) followed by a fractional part and/or an exponent part. If both a
 fractional part and exponent part are present, the fractional part must precede
@@ -338,7 +339,21 @@ underscore must be surrounded by at least one digit.
 flt8 = 9_224_617.445_991_228_313
 ```
 
-64-bit (double) precision expected.
+Float values `-0.0` and `+0.0` are valid and should map according to IEEE 754.
+
+Special float values can also be expressed. They are always lowercase.
+
+```toml
+# infinity
+sf1 = inf  # positive infinity
+sf2 = +inf # positive infinity
+sf3 = -inf # negative infinity
+
+# not a number
+sf4 = nan  # actual sNaN/qNaN encoding is implementation specific
+sf5 = +nan # same as `nan`
+sf6 = -nan # valid, actual encoding is implementation specific
+```
 
 Boolean
 -------

toml.abnf

@@ -117,14 +117,19 @@ underscore = %x5F                  ; _
 
 ;; Float
 
-float = integer ( frac / ( frac exp ) / exp )
+float = integer ( exp / frac [ exp ] )
+float =/ special-float
 
 frac = decimal-point zero-prefixable-int
 decimal-point = %x2E               ; .
 zero-prefixable-int = DIGIT *( DIGIT / underscore DIGIT )
 
 exp = "e" integer
 
+special-float = [ minus / plus ] ( inf / nan )
+inf = %x69.6e.66  ; inf
+nan = %x6e.61.6e  ; nan
+
 ;; Boolean
 
 boolean = true / false