From 3bf66ce2745cec3bb1a8ead2a6d3e2fe125bc365 Mon Sep 17 00:00:00 2001
From: malte <malte.flender@fh-bielefeld.de>
Date: Sun, 18 May 2014 18:08:36 +0200
Subject: [PATCH] POLY->ASCII: Added a function to get a string out of a given
 polynom.

---
 src/ascii_poly.c | 81 ++++++++++++++++++++++++++++++++++++------------
 src/ascii_poly.h |  1 +
 2 files changed, 63 insertions(+), 19 deletions(-)

diff --git a/src/ascii_poly.c b/src/ascii_poly.c
index e33c54f..aefaac5 100644
--- a/src/ascii_poly.c
+++ b/src/ascii_poly.c
@@ -19,18 +19,21 @@
  * MA  02110-1301  USA
  */
 
+#include "ascii_poly.h"
+#include "context.h"
+#include "err.h"
 #include "mem.h"
 #include "poly.h"
-#include "ascii_poly.h"
 
+#include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/types.h>
-#include <tompoly.h>
 #include <tommath.h>
+#include <tompoly.h>
 
-#define ASCII_DIGIETS 7
+#define ASCII_DIGITS 7
 
 /**
  * Converts a string into a pb_poly of the size strlen(to_poly) * 7.
@@ -41,34 +44,74 @@
  */
 pb_poly *ascii_to_poly(char *to_poly)
 {
-	size_t length = (strlen(to_poly) * ASCII_DIGIETS);
+	size_t length = (strlen(to_poly) * ASCII_DIGITS);
 	char *tmp_ptr = to_poly;
-	u_int8_t quotient,
-			 i,
-			 k,
-			 binary_Number[ASCII_DIGIETS + 1];
+	u_int8_t binary_Number[ASCII_DIGITS + 1];
 
-	mp_int *chara = ntru_malloc(sizeof(mp_int));
-	init_integer(chara);
+	if (!to_poly) {
+		return NULL;
+	}
+
+	mp_int chara;
+	init_integer(&chara);
 
 	pb_poly *poly = ntru_malloc(sizeof(pb_poly));
-	init_polynom_size(poly, chara, length);
+	init_polynom_size(poly, &chara, length);
 
+	/* for every char */
 	for (u_int32_t j = 0; j < strlen(to_poly); j++) {
-		quotient = (u_int8_t) *tmp_ptr++;
-		k = ASCII_DIGIETS;
-		for (i = 1; i <= ASCII_DIGIETS; i++) {
+		u_int8_t quotient = (u_int8_t) *tmp_ptr++;
+		u_int8_t k = ASCII_DIGITS;
+		for (u_int8_t i = 1; i <= ASCII_DIGITS; i++) {
+			/* gets the least significant bit in an array*/
 			binary_Number[k--] = quotient % 2;
+			/* bitshift so the next bit becomes the lsb*/
 			quotient >>= 1;
 		}
-		for (i = 1; i <= ASCII_DIGIETS; i++) {
-			mp_set(&(poly->terms[((i - 1) + (j * ASCII_DIGIETS))]),
-					binary_Number[i]);
+		for (u_int8_t i = 1; i <= ASCII_DIGITS; i++) {
+			/* the actual position of the bit in the polynom */
+			u_int32_t coefficient = (i - 1) + (j * ASCII_DIGITS);
+			MP_SET(&(poly->terms[coefficient]), binary_Number[i]);
+			/* set the array to 0 so the next run is garbage free */
 			binary_Number[i] = 0;
 			poly->terms[i].sign = 0;
 		}
 	}
 	poly->used = (int) length;
-	mp_clear(chara);
+	mp_clear(&chara);
 	return poly;
-}
\ No newline at end of file
+}
+
+/**
+ * Converts a polynom into a newly allocated string.
+ *
+ * @param to_ascii the polynom you want to make a string of.
+ * @return a pointer to the string ore a NULL pointer in the error case
+ */
+char *polynom_to_ascii(pb_poly *to_ascii)
+{
+	if (!to_ascii) {
+		return NULL;
+	}
+
+	size_t length_poly = (size_t) to_ascii->used;
+	size_t length_string = (size_t) (length_poly / ASCII_DIGITS);
+	char *string = (char*) ntru_malloc(length_string);
+	char bit_buffer;
+	char *tmp_ptr = string;
+	u_int8_t ascii_value = 0;
+
+	for (u_int32_t i = 0; i < length_poly; i += ASCII_DIGITS) {
+		for (u_int32_t j = 0; j < ASCII_DIGITS; j++) {
+			if (mp_toradix(&(to_ascii->terms[i + j]), &bit_buffer, 2)) {
+				return NULL;
+			}
+			u_int8_t bit = atoi(&bit_buffer);
+			ascii_value <<= 1;
+			ascii_value |= bit;
+		}
+		*tmp_ptr++ = ascii_value;
+		ascii_value = 0;
+	}
+	return string;
+}
diff --git a/src/ascii_poly.h b/src/ascii_poly.h
index 739801d..ee8b9d2 100644
--- a/src/ascii_poly.h
+++ b/src/ascii_poly.h
@@ -23,5 +23,6 @@
 #define ASCII_POLY_H_
 
 pb_poly *ascii_to_poly(char *to_poly);
+char *polynom_to_ascii(pb_poly *to_ascii);
 
 #endif /* ASCII_POLY_H_ */