feat(BigInt): Implement bit shifts and add math in example

1 files changed, 89 insertions, 0 deletions

diff --git a/BigInt.c b/BigInt.c
index b9239d7..4ffee57 100644
--- a/BigInt.c
+++ b/BigInt.c
@@ -74,6 +74,11 @@ B_newstr(MemoryManager *mm, const char* str) {
 }
 
 BigInt
+B_newbytes(MemoryManager *mm, usize bytes) {
+    return B_start(mm, 1 + (bytes - 1) / sizeof(UWord));
+}
+
+BigInt
 B_dup(MemoryManager *mm, BigInt bigint) {
     if (NULL == bigint)
         return NULL;
@@ -196,6 +201,90 @@ B_sub(BigInt *inta, BigInt intb) {
     return R_Ok;
 }
 
+Result
+B_rshift(BigInt *intx, usize shift) {
+    if (NULL == intx || NULL == *intx)
+        return R_NullArgument;
+
+    if (shift == 0)
+        return R_Ok;
+
+    struct BigIntMeta *bim = B_metadata(*intx);
+    UWord *x = *intx;
+
+    usize word_moves = shift / (sizeof(UWord) * 8);
+    if (word_moves) {
+        usize w = 0;
+        for (; w < bim->words - word_moves; ++w)
+            x[w] = x[w + word_moves];
+        for (; w < bim->words; ++w)
+            x[w] = 0;
+    }
+
+    usize bit_moves = shift % (sizeof(UWord) * 8);
+    if (bit_moves == 1) {
+        x[0] >>= 1;
+        for (usize w = 1; w < bim->words; ++w) {
+            x[w - 1] |= (x[w] & 1) << (sizeof(UWord) * 8 - 1);
+            x[w] >>= 1;
+        }
+    }
+    else if (bit_moves > 1) {
+        UWord mask = ((UWord)1 << bit_moves) - 1;
+
+        x[0] >>= bit_moves;
+        for (usize w = 1; w < bim->words; ++w) {
+            x[w - 1] |= (x[w] & mask) << (sizeof(UWord) * 8 - bit_moves);
+            x[w] >>= bit_moves;
+        }
+    }
+
+    return R_Ok;
+}
+
+Result
+B_lshift(BigInt *intx, usize shift) {
+    if (NULL == intx || NULL == *intx)
+        return R_NullArgument;
+
+    if (shift == 0)
+        return R_Ok;
+
+    struct BigIntMeta *bim = B_metadata(*intx);
+    UWord *x = *intx;
+
+    usize word_moves = shift / (sizeof(UWord) * 8);
+    if (word_moves) {
+        usize w = bim->words - 1;
+        for (; w >= word_moves; --w)
+            x[w] = x[w - word_moves];
+        for (; w < bim->words; --w)
+            x[w] = 0;
+    }
+
+    usize bit_moves = shift % (sizeof(UWord) * 8);
+    if (bit_moves == 1) {
+        UWord mask = (UWord)1 << (sizeof(UWord) * 8 - 1);
+
+        x[bim->words - 1] <<= 1;
+        for (usize w = bim->words - 2; w < bim->words; --w) {
+            x[w + 1] |= (x[w] & mask) >> (sizeof(UWord) * 8 - 1);
+            x[w] <<= 1;
+        }
+    }
+    else if (bit_moves > 1) {
+        UWord mask = (((UWord)1 << bit_moves) - 1) << (sizeof(UWord) * 8 - bit_moves);
+
+        x[bim->words - 1] <<= bit_moves;
+        for (usize w = bim->words - 2; w < bim->words; --w) {
+            x[w + 1] |= (x[w] & mask) >> (sizeof(UWord) * 8 - bit_moves);
+            x[w] <<= bit_moves;
+        }
+    }
+
+    return R_Ok;
+}
+
 /* Get */
 
 usize