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Pad bit-fields only to the next byte

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Fixes #1054.

Previously, bit-fields followed by another field were aligned
to two bytes.  Bit-fields ending the struct were (and continue
to be) aligned only to a single byte.

```
struct s {
  unsigned int x : 4;
};

struct t {
  unsigned int x : 4;
  unsigned int y;
};
```

Before: `sizeof(struct s) == 1`, sizeof(struct t) == 4`
After: `sizeof(struct s) == 1` sizeof(struct t) == 3`
This commit is contained in:
Jesse Rosenstock
2020-06-21 21:28:32 +02:00
committed by Oliver Schmidt
parent 9e881a497e
commit 9858e47dfd
1 changed files with 5 additions and 3 deletions
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8
src/cc65/declare.c
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@@ -772,17 +772,19 @@ static SymEntry* ParseStructDecl (const char* Name)
*/ */
if (BitOffs > 0) { if (BitOffs > 0) {
if (FieldWidth <= 0 || (BitOffs + FieldWidth) > INT_BITS) { if (FieldWidth <= 0 || (BitOffs + FieldWidth) > INT_BITS) {
/* Bits needed to byte-align the next field. */
unsigned PaddingBitWidth = -BitOffs % CHAR_BITS;
/* We need an anonymous name */ /* We need an anonymous name */
AnonName (Ident, "bit-field"); AnonName (Ident, "bit-field");
/* Add an anonymous bit-field that aligns to the next /* Add an anonymous bit-field that aligns to the next
** storage unit. ** byte.
*/ */
AddBitField (Ident, StructSize, BitOffs, INT_BITS - BitOffs); AddBitField (Ident, StructSize, BitOffs, PaddingBitWidth);
/* No bits left */ /* No bits left */
StructSize += SIZEOF_INT; StructSize += (BitOffs + PaddingBitWidth) / CHAR_BITS;
BitOffs = 0; BitOffs = 0;
} }
} }