Merge pull request #18855 from H-225/h5/fix18849

Add overloads for `bin`, `oct`, `dec` and `hex` to avoid calling `sizeof` on `BigInt`s

base/gmp.jl

@@ -518,6 +518,19 @@ oct(n::BigInt) = base( 8, n)
 dec(n::BigInt) = base(10, n)
 hex(n::BigInt) = base(16, n)
 
+for f in (:bin, :oct, :dec, :hex)
+    @eval function ($f)(n::BigInt, pad::Int)
+        b = IOBuffer()
+        res = ($f)(n)
+        diff = pad - length(res)
+        for _ in 1:diff
+            write(b, "0")
+        end
+        write(b, res)
+        String(b)
+    end
+end
+
 function base(b::Integer, n::BigInt)
     2 <= b <= 62 || throw(ArgumentError("base must be 2 ≤ base ≤ 62, got $b"))
     p = ccall((:__gmpz_get_str,:libgmp), Ptr{UInt8}, (Ptr{UInt8}, Cint, Ptr{BigInt}), C_NULL, b, &n)

test/bigint.jl

@@ -310,6 +310,20 @@ end
 @test oct(-big(9)) == "-11"
 @test hex(big(12)) == "c"
 
+# Issue #18849: bin, oct, dec, hex should not call sizeof on BigInts
+# when padding is desired
+let padding = 4, low = big(4), high = big(2^20)
+    @test bin(low, padding) == "0100"
+    @test oct(low, padding) == "0004"
+    @test dec(low, padding) == "0004"
+    @test hex(low, padding) == "0004"
+
+    @test bin(high, padding) == "100000000000000000000"
+    @test oct(high, padding) == "4000000"
+    @test dec(high, padding) == "1048576"
+    @test hex(high, padding) == "100000"
+end
+
 @test isqrt(big(4)) == 2
 @test isqrt(big(5)) == 2