Parse and encode literal integers to the right width

Affects OpConstant, and OpSwitch.

Adds constant libspirv::kUnknownType for readability.

Adds tests for hexadecimal number parsing.

Updates syntax.md to describe hex parsing, including
sign extension.

1 files changed, 11 insertions, 7 deletions

diff --git a/syntax.md b/syntax.md
index 70af1f38..7d2a4f55 100644
--- a/syntax.md
+++ b/syntax.md
@@ -27,10 +27,13 @@ but the assembler does not enforce this rule.
 
 The opcode names and expected operands are described in section 3 of
 the SPIR-V specification.  An operand is one of:
-* a literal integer: A decimal integer, or a hexadecimal integer
-  (indicated by a leading `0x`).
+* a literal integer: A decimal integer, or a hexadecimal integer.
+  A hexadecimal integer is indicated by a leading `0x` or `0X`.  A hex
+  integer supplied for a signed integer value will be sign-extended.
+  For example, `0xffff` supplied as the literal for an `OpConstant`
+  on a signed 16-bit integer type will be interpreted as the value `-1`.
 * a literal floating point number.
-* a literal string, surrounded by double-quotes ("). TODO: describe quoting and
+* a literal string, surrounded by double-quotes `"`. TODO: describe quoting and
 escaping rules.
 * a named enumerated value, specific to that operand position.  For example,
 the `OpMemoryModel` takes a named Addressing Model operand (e.g. `Logical` or
@@ -151,10 +154,11 @@ instruction.)
 The assembler processes the tokens encountered in alternate parsing mode as
 follows:
 
-* If the token is a number literal, it outputs that number as one or more words,
-  as defined in the SPIR-V specification for Literal Number.  The number must
-  fit within the unsigned 32-bit range.  All formats supported by `strtoul()`
-  are accepted.
+* If the token is a number literal, since context may be lost, the number
+  is interpreted as a 32-bit value and output as a single word.  In order to
+  specify multiple-word literals in alternate-parsing mode, further uses of
+  `!<integer>` tokens may be required.
+  All formats supported by `strtoul()` are accepted.
 * If the token is a string literal, it outputs a sequence of words representing
   the string as defined in the SPIR-V specification for Literal String.
 * If the token is an ID, it outputs the ID's internal number.