From 5337c81d6f92a301a73eda059f31c5e0c1dbdd9b Mon Sep 17 00:00:00 2001
From: Oldes <oldes.huhuman@gmail.com>
Date: Wed, 28 Dec 2022 20:55:24 +0100
Subject: [PATCH] FEAT: new `swap-endian` native function for swapping binary
 byte order

---
 src/core/f-series.c            | 69 ++++++++++++++++++++++++++++++++++
 src/tests/units/series-test.r3 | 19 ++++++++++
 2 files changed, 88 insertions(+)

diff --git a/src/core/f-series.c b/src/core/f-series.c
index e38bbe4374..55bb04c5d4 100644
--- a/src/core/f-series.c
+++ b/src/core/f-series.c
@@ -29,6 +29,7 @@
 ***********************************************************************/
 
 #include "sys-core.h"
+#include "stdio.h"
 
 #define THE_SIGN(v) ((v < 0) ? -1 : (v > 0) ? 1 : 0)
 
@@ -381,3 +382,71 @@
 	Do_Act(D_RET, VAL_TYPE(D_ARG(1)), A_POKE);
 	return R_RET;
 }
+
+/***********************************************************************
+**
+*/	REBNATIVE(swap_endian)
+/*
+//	swap-endian: native [
+//		{Swaps byte order (endianess)}
+//		value [binary!] "At position (modified)"
+//		/width bytes [integer!] "2, 4 or 8 (default is 2)"
+//		/part "Limits to a given length or position"
+//		 range [number! series!]
+]
+***********************************************************************/
+{
+	REBCNT i;
+	REBCNT width = 2;
+	REBVAL *val = D_ARG(1);
+	REBYTE *bin = VAL_BIN_DATA(D_ARG(1));
+	if (D_REF(2)) width = VAL_INT32(D_ARG(3));
+
+	REBCNT len = D_REF(4) ? Partial(val, 0, D_ARG(5), 0) : VAL_LEN(val);
+	if (len <= 0) return R_ARG1;
+
+	switch(width) {
+		case 2: {
+			uint16_t *bp = (uint16_t *)bin;
+			uint16_t  num;
+			len >>= 1;
+			for (i = 0; i < len; i++) {
+				num = bp[i];
+				bp[i] = (((num & 0x00FF) << 8) |
+				         ((num & 0xFF00) >> 8));
+			}
+			break;
+		}
+		case 4: {
+			uint32_t *bp = (uint32_t *)bin;
+			uint32_t  num;
+			len >>= 2;
+			for (i = 0; i < len; i++) {
+				num = bp[i];
+				bp[i] = (((num & 0x000000FF) << 24) |
+				         ((num & 0x0000FF00) <<  8) |
+				         ((num & 0x00FF0000) >>  8) |
+				         ((num & 0xFF000000) >> 24));
+			}
+			break;
+		}
+		case 8: {
+			uint64_t *bp = (uint64_t *)bin;
+			uint64_t  num;
+			len >>= 3;
+			for (i = 0; i < len; i++) {
+				num = bp[i];
+				num =  ((num <<  8) & 0xFF00FF00FF00FF00ULL) |
+				       ((num >>  8) & 0x00FF00FF00FF00FFULL);
+				num =  ((num << 16) & 0xFFFF0000FFFF0000ULL) |
+				       ((num >> 16) & 0x0000FFFF0000FFFFULL);
+    			bp[i] = (num << 32) | (num >> 32);
+			}
+			break;
+		}
+		default:
+			Trap1(RE_INVALID_ARG, D_ARG(3));
+	}
+
+	return R_ARG1;
+}
diff --git a/src/tests/units/series-test.r3 b/src/tests/units/series-test.r3
index df4e4f52c2..a3c6fa20f3 100644
--- a/src/tests/units/series-test.r3
+++ b/src/tests/units/series-test.r3
@@ -2504,6 +2504,25 @@ Rebol [
 
 ===end-group===
 
+
+===start-group=== "SWAP-ENDIAN"
+--test-- "swap-endian/width 2"
+	--assert #{FF00FF00FF00} = swap-endian #{00FF00FF00FF}  
+	--assert #{FF00FF00AA}   = swap-endian #{00FF00FFAA} ; the last not padded byte is ignored
+--test-- "swap-endian/width 4"
+	--assert #{4433221188776655} = swap-endian/width #{1122334455667788} 4  
+	--assert #{44332211AAAA}     = swap-endian/width #{11223344AAAA} 4
+--test-- "swap-endian/width 8"
+	--assert #{7766554433221100FFEEDDCCBBAA9988} = swap-endian/width #{00112233445566778899AABBCCDDEEFF} 8 
+	--assert #{7766554433221100AAAA}             = swap-endian/width #{0011223344556677AAAA} 8
+--test-- "swap-endian/part"
+	--assert #{FF00FF001122} = swap-endian/part #{00FF00FF1122} 4
+	--assert #{FF00FF001122} = swap-endian/part #{00FF00FF1122} 5
+	--assert #{FF00FF002211} = swap-endian/part #{00FF00FF1122} 6
+	--assert #{4433221155667788} = swap-endian/width/part #{1122334455667788} 4 4
+	--assert #{77665544332211008899AABBCCDDEEFF} = swap-endian/width/part #{00112233445566778899AABBCCDDEEFF} 8 8
+===end-group===
+
 ;-- VECTOR related tests moved to %vector-test.r3
 
 ~~~end-file~~~
\ No newline at end of file