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Stuff next three nibbles of tv_sec into top of tv_nsec to fix y2038 #38

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Stuff next three nibbles of tv_sec into top of tv_nsec to fix y2038 #38

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1 change: 1 addition & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,7 @@ It should work under any POSIX OS that support either `openpty()` or the `grantp
- Supports a no-tty mode, relying on pipes instead of pseudottys, while still recording stdout/stderr
- Automatically detects whether to use pseudottys or pipes, also overridable from command-line
- Supports reporting the number of bytes that were output to the terminal on session exit
- Format extended to support dates up to 0xFFFFFFFFFFF

## compilation

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24 changes: 14 additions & 10 deletions io.c
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Expand Up @@ -41,6 +41,7 @@
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>

Expand All @@ -65,7 +66,7 @@ static int is_little_endian(void)
char *p = (char *)&n;
char x[] = { 1, 0, 0, 0 };

assert(sizeof(int) == 4);
_Static_assert(sizeof(int) == 4, "Check relies on int size");

if (memcmp(p, x, 4) == 0)
{
Expand All @@ -81,7 +82,7 @@ static int is_little_endian(void)
}


static int convert_to_little_endian(int x)
static uint32_t convert_to_little_endian(uint32_t x)
{
if (is_little_endian())
{
Expand All @@ -96,15 +97,16 @@ static int convert_to_little_endian(int x)

int read_header(FILE *fp, Header *h)
{
int buf[3];
uint32_t buf[3], raw_usec;

if (fread_wrapper(buf, sizeof(int), 3, fp) == 0)
if (fread_wrapper(buf, sizeof(uint32_t), 3, fp) == 0)
{
return 0;
}

h->tv.tv_sec = convert_to_little_endian(buf[0]);
h->tv.tv_usec = convert_to_little_endian(buf[1]);
raw_usec = convert_to_little_endian(buf[1]);
h->tv.tv_sec = convert_to_little_endian(buf[0]) | ((raw_usec & 0xfff00000ull) << 12);
h->tv.tv_usec = raw_usec & 0x000fffffU;
h->len = convert_to_little_endian(buf[2]);

return 1;
Expand All @@ -113,13 +115,15 @@ int read_header(FILE *fp, Header *h)

int write_header(FILE *fp, Header *h)
{
int buf[3];
uint32_t buf[3];

buf[0] = convert_to_little_endian(h->tv.tv_sec);
buf[1] = convert_to_little_endian(h->tv.tv_usec);
// The reasonable range of tv_usec is [0, 999999], which is [0, 0x00`0F`42`3F]
// Thus, we can stuff 3 nibbles from tv_sec into the top bits, giving us a range of dates up to around year 559444
buf[0] = convert_to_little_endian(h->tv.tv_sec & 0xffffffffU);
buf[1] = convert_to_little_endian(h->tv.tv_usec | ((h->tv.tv_sec & 0x00000fff00000000ull) >> 12));
buf[2] = convert_to_little_endian(h->len);

if (fwrite_wrapper(buf, sizeof(int), 3, fp) == 0)
if (fwrite_wrapper(buf, sizeof(uint32_t), 3, fp) == 0)
{
return 0;
}
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