png.c: move apart non generic functions

1 files changed, 42 insertions, 0 deletions

diff --git a/png.c b/png.c
index e139bfd..2034639 100644
--- a/png.c
+++ b/png.c
@@ -4,6 +4,7 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+#include <assert.h>
 
 #define PNG_DEBUG 3
 #include <png.h>
@@ -12,6 +13,47 @@
 #define torch_Tensor TH_CONCAT_STRING_3(torch., Real, Tensor)
 #define libpng_(NAME) TH_CONCAT_3(libpng_, Real, NAME)
 
+/*
+ * Bookkeeping struct for reading png data from memory
+ */
+typedef struct {
+  unsigned char* buffer;
+  png_size_t offset;
+  png_size_t length;
+} libpng_inmem_buffer;
+
+/*
+ * Call back for reading png data from memory
+ */
+static void
+libpng_userReadData(png_structp pngPtrSrc, png_bytep dest, png_size_t length)
+{
+  libpng_inmem_buffer* src = png_get_io_ptr(pngPtrSrc);
+  assert(src->offset+length <= src->length);
+  memcpy(dest, src->buffer + src->offset, length);
+  src->offset += length;
+}
+
+/*
+ * Error message wrapper (single member struct to preserve `str` size info)
+ */
+typedef struct {
+  char str[256];
+} libpng_errmsg;
+
+/*
+ * Custom error handling function (see `png_set_error_fn`)
+ */
+static void
+libpng_error_fn(png_structp png_ptr, png_const_charp error_msg)
+{
+  libpng_errmsg *errmsg = png_get_error_ptr(png_ptr);
+  int max = sizeof(errmsg->str) - 1;
+  strncpy(errmsg->str, error_msg, max);
+  errmsg->str[max] = '\0';
+  longjmp(png_jmpbuf(png_ptr), 1);
+}
+
 #include "generic/png.c"
 #include "THGenerateAllTypes.h"