diff options
| -rw-r--r-- | fitz/stm_buffer.c | 72 |
1 files changed, 66 insertions, 6 deletions
diff --git a/fitz/stm_buffer.c b/fitz/stm_buffer.c index 7a676a67..706be39a 100644 --- a/fitz/stm_buffer.c +++ b/fitz/stm_buffer.c @@ -110,9 +110,13 @@ void fz_write_buffer_byte(fz_context *ctx, fz_buffer *buf, int val) void fz_write_buffer_bits(fz_context *ctx, fz_buffer *buf, int val, int bits) { - int extra; int shift; + /* Throughout this code, the invariant is that we need to write the + * bottom 'bits' bits of 'val' into the stream. On entry we assume + * that val & ((1<<bits)-1) == val, but we do not rely on this after + * having written the first partial byte. */ + if (bits == 0) return; @@ -121,12 +125,16 @@ void fz_write_buffer_bits(fz_context *ctx, fz_buffer *buf, int val, int bits) * buf->unused_bits = the number of unused bits in the last byte. */ - /* Extend the buffer as required before we start; that way we never - * fail part way during writing. */ + /* Find the amount we need to shift val up by so that it will be in + * the correct position to be inserted into any existing data byte. */ shift = (buf->unused_bits - bits); + + /* Extend the buffer as required before we start; that way we never + * fail part way during writing. If shift < 0, then we'll need -shift + * more bits. */ if (shift < 0) { - extra = (7-buf->unused_bits)>>3; + int extra = (7-shift)>>3; /* Round up to bytes */ fz_ensure_buffer(ctx, buf, buf->len + extra); } @@ -135,8 +143,14 @@ void fz_write_buffer_bits(fz_context *ctx, fz_buffer *buf, int val, int bits) { buf->data[buf->len-1] |= (shift >= 0 ? (((unsigned int)val)<<shift) : (((unsigned int)val)>>-shift)); if (shift >= 0) + { + /* If we were shifting up, we're done. */ + buf->unused_bits -= bits; return; - bits += shift; + } + /* The number of bits left to write is the number that didn't + * fit in this first byte. */ + bits = -shift; } /* Write any whole bytes */ @@ -149,7 +163,7 @@ void fz_write_buffer_bits(fz_context *ctx, fz_buffer *buf, int val, int bits) /* Write trailing bits (with 0's in unused bits) */ if (bits > 0) { - bits += 8; + bits = 8-bits; buf->data[buf->len++] = val<<bits; } buf->unused_bits = bits; @@ -174,3 +188,49 @@ fz_buffer_printf(fz_context *ctx, fz_buffer *buffer, char *fmt, ...) va_end(args); } + +#ifdef TEST_BUFFER_WRITE + +#define TEST_LEN 1024 + +void +fz_test_buffer_write(fz_context *ctx) +{ + fz_buffer *master = fz_new_buffer(ctx, TEST_LEN); + fz_buffer *copy = fz_new_buffer(ctx, TEST_LEN); + fz_stream *stm; + int i, j, k; + + /* Make us a dummy buffer */ + for (i = 0; i < TEST_LEN; i++) + { + master->data[i] = rand(); + } + master->len = TEST_LEN; + + /* Now copy that buffer several times, checking it for validity */ + stm = fz_open_buffer(ctx, master); + for (i = 0; i < 256; i++) + { + memset(copy->data, i, TEST_LEN); + copy->len = 0; + j = TEST_LEN * 8; + do + { + k = (rand() & 31)+1; + if (k > j) + k = j; + fz_write_buffer_bits(ctx, copy, fz_read_bits(stm, k), k); + j -= k; + } + while (j); + + if (memcmp(copy->data, master->data, TEST_LEN) != 0) + fprintf(stderr, "Copied buffer is different!\n"); + fz_seek(stm, 0, 0); + } + fz_close(stm); + fz_drop_buffer(ctx, master); + fz_drop_buffer(ctx, copy); +} +#endif |