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ICU-65 make OffsetIndex.gmtOffset 4-aligned

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X-SVN-Rev: 410
This commit is contained in:
Alan Liu 1999-12-14 20:17:02 +00:00
parent 4694b93a81
commit 6da447a09e
2 changed files with 31 additions and 14 deletions
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15
icu4c/source/i18n/tzdat.h
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@ -127,14 +127,25 @@ struct DSTZone {
* discriminating information. This information comes from the file
* tz.default. Note that this is itself a zone number, like
* those in the array starting at &zoneNumber.
*
* The gmtOffset field must be 4-aligned for some architectures. To
* ensure this, we do two things: 1. The entire struct is 4-aligned.
* 2. The gmtOffset is placed at a 4-aligned position within the
* struct. 3. The size of the whole structure is padded out to 4n
* bytes. We achieve this last condition by adding two bytes of
* padding after the last zoneNumber, if count is _even_. That is,
* the struct size is 10+2count+padding, where padding is (count%2==0
* ? 2:0). See gentz for implementation.
*/
struct OffsetIndex {
int32_t gmtOffset; // in ms
int32_t gmtOffset; // in ms - 4-aligned
uint16_t nextEntryDelta;
uint16_t defaultZone; // a zone number from 0..TZHeader.count-1
uint16_t count;
uint16_t padding; // to make the next field 32-bit aligned
uint16_t zoneNumber; // There are actually 'count' uint16_t's here
// Following the 'count' uint16_t's starting with zoneNumber,
// there may be two bytes of padding to make the whole struct have
// a size of 4n. nextEntryDelta skips over any padding.
};
// Information used to identify and validate the data

30
icu4c/source/tools/gentz/gentz.cpp
View file

@ -333,12 +333,17 @@ OffsetIndex* gentz::parseOffsetIndexTable(FileStream* in) {
// We don't know how big the whole thing will be yet, but we can use
// the maxPerOffset number to compute an upper limit.
//
// Structs MUST be 4-aligned. We accomplish this by
// (a) a padding byte before the zoneNumber field
// in the OffsetIndex structure and
//
// (b) rounding index->count to the least greatest
// even number.
// The gmtOffset field within each OffsetIndex struct must be
// 4-aligned for some architectures. To ensure this, we do two
// things: 1. The entire struct is 4-aligned. 2. The gmtOffset is
// placed at a 4-aligned position within the struct. 3. The size
// of the whole structure is padded out to 4n bytes. We achieve
// this last condition by adding two bytes of padding after the
// last zoneNumber, if count is _even_. That is, the struct size
// is 10+2count+padding, where padding is (count%2==0 ? 2:0).
//
// Note that we don't change the count itself, but rather adjust
// the nextEntryDelta and add 2 bytes of padding if necessary.
//
// Don't try to compute the exact size in advance
// (unless we want to avoid the use of sizeof(), which may
@ -354,7 +359,7 @@ OffsetIndex* gentz::parseOffsetIndexTable(FileStream* in) {
// Read each line and construct the corresponding entry
OffsetIndex* index = (OffsetIndex*)result;
for (uint32_t i=0; i<n; ++i) {
uint16_t alignedCount;
uint16_t alignedCount;
readLine(in);
char* p = buffer;
index->gmtOffset = 1000 * // Convert s -> ms
@ -374,11 +379,12 @@ OffsetIndex* gentz::parseOffsetIndexTable(FileStream* in) {
if (!sawOffset) {
die("Error: bad offset index entry; default not in zone list");
}
alignedCount = index->count;
if((alignedCount%2)==1) /* force count to be even (thus 32 bit aligned)*/
{
alignedCount++;
}
alignedCount = index->count;
if((alignedCount%2)==0) /* force count to be ODD - see above */
{
// Use invalid zoneNumber for 2 bytes of padding
zoneNumberArray[alignedCount++] = (uint16_t)0xFFFF;
}
int8_t* nextIndex = (int8_t*)&(zoneNumberArray[alignedCount]);
index->nextEntryDelta = (i==(n-1)) ? 0 : (nextIndex - (int8_t*)index);