Fix sign and conversion warnings (major)

This makes all integer type conversions that have potential data loss
explicit with calls that do range checks and raise an exception. After
this commit, qpdf builds with no warnings when -Wsign-conversion
-Wconversion is used with gcc or clang or when -W3 -Wd4800 is used
with MSVC. This significantly reduces the likelihood of potential
crashes from bogus integer values.

There are some parts of the code that take int when they should take
size_t or an offset. Such places would make qpdf not support files
with more than 2^31 of something that usually wouldn't be so large. In
the event that such a file shows up and is valid, at least qpdf would
raise an error in the right spot so the issue could be legitimately
addressed rather than failing in some weird way because of a silent
overflow condition.

2 files changed, 6 insertions, 6 deletions

diff --git a/libqpdf/sph/md_helper.c b/libqpdf/sph/md_helper.c
index 5384f03f..829391a7 100644
--- a/libqpdf/sph/md_helper.c
+++ b/libqpdf/sph/md_helper.c
@@ -145,7 +145,7 @@ SPH_XCAT(sph_, HASH)(void *cc, const void *data, size_t len)
 
 		clen = SPH_BLEN - current;
 		if (clen > len)
-			clen = len;
+			clen = (unsigned)len;
 		memcpy(sc->buf + current, data, clen);
 		data = (const unsigned char *)data + clen;
 		current += clen;
@@ -257,7 +257,7 @@ SPH_XCAT(HASH, _addbits_and_close)(void *cc,
 	{
 		unsigned z;
 
-		z = 0x80 >> n;
+		z = 0x80U >> n;
 		sc->buf[current ++] = ((ub & -z) | z) & 0xFF;
 	}
 #endif
diff --git a/libqpdf/sph/sph_types.h b/libqpdf/sph/sph_types.h
index f434d8bb..e3b648c1 100644
--- a/libqpdf/sph/sph_types.h
+++ b/libqpdf/sph/sph_types.h
@@ -1337,8 +1337,8 @@ sph_bswap64(sph_u64 x)
 static SPH_INLINE void
 sph_enc16be(void *dst, unsigned val)
 {
-	((unsigned char *)dst)[0] = (val >> 8);
-	((unsigned char *)dst)[1] = val;
+	((unsigned char *)dst)[0] = (unsigned char)(val >> 8);
+	((unsigned char *)dst)[1] = (unsigned char)val;
 }
 
 static SPH_INLINE unsigned
@@ -1351,8 +1351,8 @@ sph_dec16be(const void *src)
 static SPH_INLINE void
 sph_enc16le(void *dst, unsigned val)
 {
-	((unsigned char *)dst)[0] = val;
-	((unsigned char *)dst)[1] = val >> 8;
+	((unsigned char *)dst)[0] = (unsigned char)val;
+	((unsigned char *)dst)[1] = (unsigned char)(val >> 8);
 }
 
 static SPH_INLINE unsigned