R magic number from the R source

Implements the writing/reading of the version and format of an RData file or blob.

src/Rmagic.c

@@ -0,0 +1,106 @@
+#include "Rmagic.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int R_WriteMagic(FILE *fp, int number)
+{
+  unsigned char buf[5];
+  size_t res;
+
+  number = abs(number);
+  switch (number) {
+    case R_MAGIC_ASCII_V1:   /* Version 1 - R Data, ASCII Format */
+      strcpy((char*)buf, "RDA1");
+    break;
+    case R_MAGIC_BINARY_V1:  /* Version 1 - R Data, Binary Format */
+      strcpy((char*)buf, "RDB1");
+    break;
+    case R_MAGIC_XDR_V1:     /* Version 1 - R Data, XDR Binary Format */
+      strcpy((char*)buf, "RDX1");
+    break;
+    case R_MAGIC_ASCII_V2:   /* Version 2 - R Data, ASCII Format */
+      strcpy((char*)buf, "RDA2");
+    break;
+    case R_MAGIC_BINARY_V2:  /* Version 2 - R Data, Binary Format */
+      strcpy((char*)buf, "RDB2");
+    break;
+    case R_MAGIC_XDR_V2:     /* Version 2 - R Data, XDR Binary Format */
+      strcpy((char*)buf, "RDX2");
+    break;
+    case R_MAGIC_ASCII_V3:   /* Version >=3 - R Data, ASCII Format */
+      strcpy((char*)buf, "RDA3");
+    break;
+    case R_MAGIC_BINARY_V3:  /* Version >=3 - R Data, Binary Format */
+      strcpy((char*)buf, "RDB3");
+    break;
+    case R_MAGIC_XDR_V3:     /* Version >=3 - R Data, XDR Binary Format */
+      strcpy((char*)buf, "RDX3");
+    break;
+    default:
+      buf[0] = (unsigned char)((number / 1000) % 10 + '0');
+      buf[1] = (unsigned char)((number / 100) % 10 + '0');
+      buf[2] = (unsigned char)((number / 10) % 10 + '0');
+      buf[3] = (unsigned char)(number % 10 + '0');
+  }
+  buf[4] = '\n';
+
+  res = fwrite((char*)buf, sizeof(char), 5, fp);
+  if(res != 5) {
+    return -1;
+  }
+  return 0;
+}
+
+int R_ReadMagic(FILE *fp)
+{
+  unsigned char buf[6];
+  int d1, d2, d3, d4;
+  size_t count;
+
+  count = fread((char*)buf, sizeof(char), 5, fp);
+  if (count != 5) {
+    if (count == 0) {
+      return R_MAGIC_EMPTY;
+    } else {
+      return R_MAGIC_CORRUPT;
+    }
+  }
+ 
+  /* Version 1 */
+  if (strncmp((char*)buf, "RDA1\n", 5) == 0) {
+    return R_MAGIC_ASCII_V1;
+  } else if (strncmp((char*)buf, "RDB1\n", 5) == 0) {
+    return R_MAGIC_BINARY_V1;
+  } else if (strncmp((char*)buf, "RDX1\n", 5) == 0) {
+    return R_MAGIC_XDR_V1;
+  }
+
+  /* Version 2 */
+  if (strncmp((char*)buf, "RDA2\n", 5) == 0) {
+    return R_MAGIC_ASCII_V2;
+  } else if (strncmp((char*)buf, "RDB2\n", 5) == 0) {
+    return R_MAGIC_BINARY_V2;
+  } else if (strncmp((char*)buf, "RDX2\n", 5) == 0) {
+    return R_MAGIC_XDR_V2;
+  }
+
+  /* Version 3 */
+  if (strncmp((char*)buf, "RDA3\n", 5) == 0) {
+    return R_MAGIC_ASCII_V3;
+  } else if (strncmp((char*)buf, "RDB3\n", 5) == 0) {
+    return R_MAGIC_BINARY_V3;
+  } else if (strncmp((char*)buf, "RDX3\n", 5) == 0) {
+    return R_MAGIC_XDR_V3;
+  } else if (strncmp((char *)buf, "RD", 2) == 0) {
+    return R_MAGIC_MAYBE_TOONEW;
+  }
+
+  /* Intel gcc seems to screw up a single expression here */
+  d1 = (buf[3] - '0') % 10;
+  d2 = (buf[2] - '0') % 10;
+  d3 = (buf[1] - '0') % 10;
+  d4 = (buf[0] - '0') % 10;
+  return d1 + 10 * d2 + 100 * d3 + 1000 * d4;
+}

src/Rmagic.h

@@ -0,0 +1,32 @@
+#ifndef __R_MAGIC_H__
+#define __R_MAGIC_H__
+
+#include <stdio.h>
+
+#define R_STREAM_VERSION 3
+
+#define R_MAGIC_ASCII_V3   3001
+#define R_MAGIC_BINARY_V3  3002
+#define R_MAGIC_XDR_V3     3003
+#define R_MAGIC_ASCII_V2   2001
+#define R_MAGIC_BINARY_V2  2002
+#define R_MAGIC_XDR_V2     2003
+#define R_MAGIC_ASCII_V1   1001
+#define R_MAGIC_BINARY_V1  1002
+#define R_MAGIC_XDR_V1     1003
+#define R_MAGIC_EMPTY      999
+#define R_MAGIC_CORRUPT    998
+#define R_MAGIC_MAYBE_TOONEW 997
+
+/* pre-1 formats (R < 0.99.0) */
+#define R_MAGIC_BINARY 1975
+#define R_MAGIC_ASCII  1976
+#define R_MAGIC_XDR    1977
+#define R_MAGIC_BINARY_VERSION16 1971
+#define R_MAGIC_ASCII_VERSION16  1972
+
+int R_WriteMagic(FILE *fp, int number);
+
+int R_ReadMagic(FILE *fp);
+
+#endif // __R_MAGIC_H__