From 7e0b603b78adf4c1704b757da05d085e03afe5f6 Mon Sep 17 00:00:00 2001
From: Syndamia <kamen@syndamia.com>
Date: Sat, 23 May 2026 09:56:17 +0300
Subject: feat(BigInt): Implement bit shifts and add math in example

---
 BigInt.c  | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 BigInt.h  |  3 +++
 example.c | 26 +++++++++++++++++++
 3 files changed, 118 insertions(+)

diff --git a/BigInt.c b/BigInt.c
index b9239d7..4ffee57 100644
--- a/BigInt.c
+++ b/BigInt.c
@@ -73,6 +73,11 @@ B_newstr(MemoryManager *mm, const char* str) {
     return NULL;
 }
 
+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)
@@ -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
diff --git a/BigInt.h b/BigInt.h
index 2324143..913e249 100644
--- a/BigInt.h
+++ b/BigInt.h
@@ -9,6 +9,7 @@ typedef void* BigInt;
 
 BigInt B_new(MemoryManager *mm, int value);
 BigInt B_newstr(MemoryManager *mm, const char* str);
+BigInt B_newbytes(MemoryManager *mm, usize bytes);
 BigInt B_dup(MemoryManager *mm, BigInt bigint);
 
 BigInt B_newsum(MemoryManager *mm, BigInt a, BigInt b);
@@ -22,6 +23,8 @@ Result B_free(BigInt *bigint);
 
 Result B_sum(BigInt *a, BigInt b);
 Result B_sub(BigInt *a, BigInt b);
+Result B_rshift(BigInt *x, usize shift);
+Result B_lshift(BigInt *x, usize shift);
 
 /* Get */
 
diff --git a/example.c b/example.c
index 6dc3525..52d402e 100644
--- a/example.c
+++ b/example.c
@@ -3,6 +3,7 @@
 #include "Vector.h"
 #include "String.h"
 #include "BumpAlloc.h"
+#include "BigInt.h"
 #include <stdio.h>
 
 int
@@ -42,6 +43,31 @@ main() {
     PRINT_NOTOK(H_freevals(&tet));
     PRINT_NOTOK(H_free(&tet));
 
+    BigInt a = B_new(&g, -1),
+           b = B_new(&g, 1);
+
+    {
+        uint_fast32_t *aa = a;
+        aa[0] = -1;
+    }
+
+    B_sum(&a, b);
+    char *astr = B_tostr(&g, a);
+    printf("a + b = %s\n", astr);
+
+    B_sub(&a, b);
+    B_sub(&a, b);
+    astr = B_tostr(&g, a);
+    printf("a - b = %s\n", astr);
+
+    B_lshift(&a, 30);
+    astr = B_tostr(&g, a);
+    printf("a << 30 = %s\n", astr);
+
+    B_rshift(&a, 30);
+    astr = B_tostr(&g, a);
+    printf("a >> 30 = %s\n", astr);
+
     PRINT_NOTOK(g.destroy(&g));
     PRINT_NOTOK(t.destroy(&t));
     PRINT_NOTOK(T.destroy(&T));
-- 
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