From 93ebab379bf9f3bd3948b263da7362cfc07abc5e Mon Sep 17 00:00:00 2001
From: Kevin Cotugno <kevin@kevincotugno.com>
Date: Wed, 10 Oct 2018 16:40:47 -0700
Subject: [PATCH] WIP

---
 c/big_int.c | 80 +++++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 66 insertions(+), 14 deletions(-)

diff --git a/c/big_int.c b/c/big_int.c
index 4d52469..ea3796f 100644
--- a/c/big_int.c
+++ b/c/big_int.c
@@ -26,13 +26,23 @@
 #define LSHIFT32(x) (x << BIT_SIZE)
 #define RSHIFT32(x) (x >> BIT_SIZE)
 
+#define SWAP(x, y) { void *tmp = x; x = y, y = tmp; }
+
+typedef unsigned BOOL;
+
 struct big_int {
 	uint64_t count;
 	uint64_t size;
 	uint32_t* buf;
 };
 
-void big_int_grow(struct big_int* i, int copy);
+struct big_int* big_int_init(uint64_t x);
+void big_int_destroy(struct big_int* i);
+void big_int_internal_grow(struct big_int* i, size_t size, BOOL copy);
+void big_int_grow(struct big_int* i, BOOL copy);
+uint64_t big_int_bit_len(struct big_int* i);
+void big_int_add(struct big_int *a, struct big_int *b);
+void big_int_sub(struct big_int* a, struct big_int* b);
 
 struct big_int* big_int_init(uint64_t x)
 {
@@ -53,28 +63,32 @@ void big_int_destroy(struct big_int* i)
 	free(i);
 }
 
-void big_int_grow(struct big_int* i, int copy)
+void big_int_internal_grow(struct big_int* i, size_t size, BOOL copy)
 {
 	uint32_t* tmp;
-	size_t new_size = (size_t)i->size * MEM_STEPS;
-
-	tmp = (uint32_t*)calloc(new_size, sizeof(uint32_t));
-
-	if (copy)
-		memcpy(tmp, i->buf, sizeof(uint32_t) * (size_t)i->size);
+	tmp = (uint32_t*)calloc(size, sizeof(uint32_t) * size);
 
 	if (tmp == NULL) {
 		printf("Unable to allocate memory");
 		exit(1);
 	}
 
+	if (copy)
+		memcpy(tmp, i->buf, sizeof(uint32_t) * (size_t)i->size);
+
 	i->buf = tmp;
-	i->size = new_size;
+	i->size = size;
+}
+
+void big_int_grow(struct big_int* i, BOOL copy)
+{
+	size_t new_size = (size_t)i->size * MEM_STEPS;
+	big_int_internal_grow(i, new_size, copy);
 }
 
 uint64_t big_int_bit_len(struct big_int* i)
 {
-	uint64_t j = 32;
+	uint32_t j = 32;
 	uint32_t x = i->buf[i->count - 1];
 
 	if (x <= 0x0000ffff) j -= 16, x <<= 16;
@@ -121,12 +135,11 @@ void big_int_add(struct big_int *a, struct big_int *b)
 		i++;
 	} while(i < a->count || i < b->count || carry > 0);
 
-	uint32_t* tmp_ptr = a->buf;
-	a->buf = result->buf;
+	SWAP(a->buf, result->buf);
 	a->count = i;
 	a->size = result->size;
 
-	free(tmp_ptr);
+	big_int_destroy(result);
 }
 
 void big_int_add_uint32(struct big_int* a, uint32_t b)
@@ -134,19 +147,58 @@ void big_int_add_uint32(struct big_int* a, uint32_t b)
 	big_int_add(a, big_int_init(b));
 }
 
+void big_int_sub(struct big_int* a, struct big_int* b)
+{
+	struct big_int* result = big_int_init(0);
+	uint64_t tmp = 0;
+	uint64_t carry = 0;
+
+	uint64_t i = a->count + 2;
+	do {
+		uint64_t x = 0, y = 0;
+
+		if (i - 2 < a->count) {
+			x = (uint64_t)a->buf[i - 2];
+		}
+
+		x |= carry;
+
+		if (i - 2 < b->count) {
+			y = (uint64_t)b->buf[i - 2];
+		}
+
+		tmp = x - y;
+		result->buf[i - 1] = (uint32_t)RSHIFT32(UPPER64(tmp));
+		carry = LSHIFT32(LOWER64(tmp));
+
+		--i;
+	} while(i > 0);
+
+	SWAP(a->buf, result->buf);
+	a->size = result->size;
+
+	big_int_destroy(result);
+}
+
 int main(void)
 {
 	struct big_int* bi = big_int_init(123456789);
 
 	big_int_add_uint32(bi, 123456789);
 
-	for (int i = 0; i < 1000; i++)
+	for (int i = 0; i < 10; i++)
 		big_int_add(bi, bi);
 
 	for (uint64_t i = 0; i < bi->count; i++)
 		printf("[%" PRIu32 "] ", bi->buf[i]);
 	printf("\n");
 
+	big_int_sub(bi, big_int_init(53350));
+
+	for (uint64_t i = 0; i < bi->count; i++)
+		printf("[%" PRIu32 "] ", bi->buf[i]);
+	printf("\n");
+
 	printf("%lu\n", big_int_bit_len(bi));
 	printf("%" PRIu64 "\n", bi->size);