1 files changed, 22 insertions, 0 deletions
diff --git a/aoc-2025/utils/parse.asm b/aoc-2025/utils/parse.asm
new file mode 100644
index 0000000..833cb4e
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+++ b/aoc-2025/utils/parse.asm
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+; utils/parse.asm - decimal parsing helper.
+
+section .text
+
+; parse_u64: read decimal digits at [RSI] into RAX, advancing RSI past them.
+; Stops on the first non-digit. Clobbers RAX, RDX.
+parse_u64:
+    xor     rax, rax
+.digit:
+    mov     dl, [rsi]
+    cmp     dl, '0'
+    jl      .done
+    cmp     dl, '9'
+    jg      .done
+    sub     dl, '0'
+    movzx   rdx, dl
+    imul    rax, rax, 10
+    add     rax, rdx
+    inc     rsi
+    jmp     .digit
+.done:
+    ret