move the R implementation of base64 encoding from knitr (yihui/knitr#324

) to xfun

R/base64.R

@@ -14,6 +14,37 @@ base64_encode = function(x) {
   .Call('base64_enc', x)
 }
 
+# an R implementation of base64 encoding by Wush Wu moved from knitr (of
+# historic interest only): https://github.com/yihui/knitr/pull/324
+base64_encode_r = function(raw.string) {
+  chars = c(LETTERS, letters, 0:9, '+', '/')
+  n = length(s <- as.integer(raw.string))
+  res = rep(NA, (n + 2) / 3 * 4)
+  i = 0L  # index of res vector
+  j = 1L  # index of base64_table
+  while (n > 2L) {
+    res[i <- i + 1L] = chars[s[j] %/% 4L + 1L]
+    res[i <- i + 1L] = chars[16 * (s[j] %% 4L) + s[j + 1L] %/% 16 + 1L]
+    res[i <- i + 1L] = chars[4L * (s[j + 1L] %% 16) + s[j + 2L] %/% 64L + 1L]
+    res[i <- i + 1L] = chars[s[j + 2L] %% 64L + 1L]
+    j = j + 3L
+    n = n - 3L
+  }
+  if (n) {
+    res[i <- i + 1L] = chars[s[j] %/% 4L + 1L]
+    if (n > 1L) {
+      res[i <- i + 1L] = chars[16 * (s[j] %% 4L) + s[j + 1L] %/% 16 + 1L]
+      res[i <- i + 1L] = chars[4L * (s[j + 1L] %% 16) + 1L]
+      res[i <- i + 1L] = '='
+    } else {
+      res[i <- i + 1L] = chars[16 * (s[j] %% 4L) + 1L]
+      res[i <- i + 1L] = '='
+      res[i <- i + 1L] = '='
+    }
+  }
+  paste(res[!is.na(res)], collapse = '')
+}
+
 #' Generate the Data URI for a file
 #'
 #' Encode the file in the base64 encoding, and add the media type. The data URI