From 9d0f0b2c714819d93eb29f0f00fd5aa600da880f Mon Sep 17 00:00:00 2001
From: Syndamia <kamen@syndamia.com>
Date: Wed, 27 May 2026 15:07:20 +0300
Subject: feat: Implement B_newstr

---
 BigInt.c  | 50 +++++++++++++++++++++++++++++++++++++++++++++++---
 example.c |  4 ++++
 2 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/BigInt.c b/BigInt.c
index d5b1d20..e0014cc 100644
--- a/BigInt.c
+++ b/BigInt.c
@@ -2,6 +2,7 @@
 #include "MemoryManager.h"
 #include "Types.h"
 #include <limits.h>
+#include <stdio.h>
 #include <string.h>
 
 typedef uint_fast32_t UWord;
@@ -72,11 +73,54 @@ B_new(MemoryManager *mm, int value) {
 
 BigInt
 B_newstr(MemoryManager *mm, const char* str) {
-    return NULL;
+    if (NULL == str)
+        return NULL;
+
+    usize len = strlen(str);
+
+    UWord *num = B_newbytes(mm, len / 2);
+    if (NULL == num)
+        return NULL;
+
+    UWord *bcd = B_newbytes(mm, len / 2);
+    if (NULL == bcd) {
+        mm->free(*mm, (void**)&num);
+        return NULL;
+    }
+
+    struct BigIntMeta *numm = B_metadata(num);
+    struct BigIntMeta *bcdm = B_metadata(bcd);
+
+    // char string to BCD
+    for (const char *s = str; *s != '\0'; ++s) {
+        B_lshift((BigInt*)&bcd, 4);
+        bcd[0] |= *s - '0';
+    }
+
+    // Double-dable bcd to BigInt
+    for (usize i = len * 4; i > 0; --i) {
+        B_rshift((BigInt*)&num, 1);
+        num[numm->words - 1] |= (UWord)(bcd[0] & 1) << (UWORD_BIT - 1);
+        B_rshift((BigInt*)&bcd, 1);
+
+        for (usize w = 0; w < bcdm->words; ++w) {
+            for (UWord mask = 0b1111, eight = 8, three = 3; mask > 0; mask <<= 4, eight <<= 4, three <<= 4) {
+                if ((bcd[w] & mask) >= eight)
+                    bcd[w] -= three;
+            }
+        }
+    }
+    B_rshift((BigInt*)&num, UWORD_BIT * numm->words - len * 4);
+
+    mm->free(*mm, (void**)&bcd);
+
+    return num;
 }
 
 BigInt
 B_newbytes(MemoryManager *mm, usize bytes) {
+    if (0 == bytes)
+        return B_start(mm, 1);
     return B_start(mm, 1 + (bytes - 1) / sizeof(UWord));
 }
 
@@ -214,7 +258,7 @@ B_rshift(BigInt *intx, usize shift) {
     struct BigIntMeta *bim = B_metadata(*intx);
     UWord *x = *intx;
 
-    usize word_moves = shift / (sizeof(UWord) * CHAR_BIT);
+    usize word_moves = shift / UWORD_BIT;
     if (word_moves) {
         usize w = 0;
         for (; w < bim->words - word_moves; ++w)
@@ -357,7 +401,7 @@ B_tostr(MemoryManager *mm, BigInt intx) {
     }
     memset(bcd, 0, sizeof(u8) * bcd_bytes);
 
-    UWord mask = (UWord)1 << (sizeof(UWord) * 8 - 1);
+    UWord mask = (UWord)1 << (UWORD_BIT - 1);
 
     // Double-dable, binary to binary-coded decimal
     for (usize w = bim->words - 1; w < bim->words; --w) {
diff --git a/example.c b/example.c
index 52d402e..420264a 100644
--- a/example.c
+++ b/example.c
@@ -68,6 +68,10 @@ main() {
     astr = B_tostr(&g, a);
     printf("a >> 30 = %s\n", astr);
 
+    BigInt c = B_newstr(&g, "12345678901234567890123");
+    astr = B_tostr(&g, c);
+    printf("c = %s\n", astr);
+
     PRINT_NOTOK(g.destroy(&g));
     PRINT_NOTOK(t.destroy(&t));
     PRINT_NOTOK(T.destroy(&T));
-- 
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