From fb0daad20211a8f5acc9f870c70cf130e011ec19 Mon Sep 17 00:00:00 2001
From: Oldes <oldes.huhuman@gmail.com>
Date: Wed, 6 Oct 2021 19:02:20 +0200
Subject: [PATCH] FEAT: new `ATz` action returning the seriest at 0-based
 position (index) CHANGE: `at` action on image with pair position was 0-based,
 now is 1-based

related to: https://github.com/Oldes/Rebol-issues/issues/613
---
 src/boot/actions.reb           |  6 ++++
 src/core/f-series.c            | 14 ++-------
 src/core/t-gob.c               |  1 +
 src/core/t-image.c             | 13 ++++----
 src/tests/units/gob-test.r3    |  2 ++
 src/tests/units/image-test.r3  | 55 +++++++++++++++++++++++++++-------
 src/tests/units/series-test.r3 | 16 ++++++++++
 7 files changed, 77 insertions(+), 30 deletions(-)

diff --git a/src/boot/actions.reb b/src/boot/actions.reb
index 29b92125c3..d13d458f0b 100644
--- a/src/boot/actions.reb
+++ b/src/boot/actions.reb
@@ -170,6 +170,12 @@ at: action [
 	index [number! logic! pair!]
 ]
 
+atz: action [
+	{Returns the series at the specified 0-based index.}
+	series [series! gob! port!]
+	index [number! logic! pair!]
+]
+
 index?: action [
 	{Returns the current position (index) of the series.}
 	series [series! gob! port! none!]
diff --git a/src/core/f-series.c b/src/core/f-series.c
index 70d16e174c..36353fd345 100644
--- a/src/core/f-series.c
+++ b/src/core/f-series.c
@@ -80,12 +80,13 @@
 
 	case A_SKIP:
 	case A_AT:
+	case A_ATZ:
 		len = Get_Num_Arg(arg);
 		{
 			REBI64 i = (REBI64)index + (REBI64)len;
 			if (action == A_SKIP) {
 				if (IS_LOGIC(arg)) i--;
-			} else { // A_AT
+			} else if (action == A_AT) {
 				if (len > 0) i--;
 			}
 			if (i > (REBI64)tail) i = (REBI64)tail;
@@ -93,16 +94,7 @@
 			VAL_INDEX(value) = (REBCNT)i;
 		}
 		break;
-/*
-	case A_ATZ:
-		len = Get_Num_Arg(arg);
-		{
-			REBI64 idx = Add_Max(0, index, len, MAX_I32);
-			if (idx < 0) idx = 0;
-			VAL_INDEX(value) = (REBCNT)idx;
-		}
-		break;
-*/
+
 	case A_INDEXQ:
 		SET_INTEGER(DS_RETURN, ((REBI64)index) + 1);
 		return R_RET;
diff --git a/src/core/t-gob.c b/src/core/t-gob.c
index 8fd8d0e4d6..b5ad8fca8c 100644
--- a/src/core/t-gob.c
+++ b/src/core/t-gob.c
@@ -910,6 +910,7 @@ const REBCNT Gob_Flag_Words[] = {
 	case A_AT:
 		index--;
 	case A_SKIP:
+	case A_ATZ:
 		index += VAL_INT32(arg);
 		goto set_index;
 
diff --git a/src/core/t-image.c b/src/core/t-image.c
index 76ad1fe3fa..faebe80516 100644
--- a/src/core/t-image.c
+++ b/src/core/t-image.c
@@ -1070,21 +1070,18 @@ INLINE REBCNT ARGB_To_BGR(REBCNT i)
 		Pick_Path(value, arg, D_ARG(3));
 		return R_ARG3;
 
-	case A_SKIP:
-	case A_AT:
-		// This logic is somewhat complicated by the fact that INTEGER args use
-		// base-1 indexing, but PAIR args use base-0.
+	case A_AT:   // base-1
+	case A_ATZ:  // base-0
+	case A_SKIP: // base-0
 		if (IS_PAIR(arg)) {
-			if (action == A_AT) action = A_SKIP;
-			diff = (VAL_PAIR_Y_INT(arg) * VAL_IMAGE_WIDE(value) + VAL_PAIR_X_INT(arg)) +
-				((action == A_SKIP) ? 0 : 1);
+			diff = ((VAL_PAIR_Y_INT(arg) - ((action == A_AT) ? 1 : 0)) * VAL_IMAGE_WIDE(value) + VAL_PAIR_X_INT(arg));
 		} else
 			diff = Get_Num_Arg(arg);
 
 		index += diff;
 		if (action == A_SKIP) {
 			if (IS_LOGIC(arg)) index--;
-		} else {
+		} else if (action == A_AT) {
 			if (diff > 0) index--; // For at, pick, poke.
 		}
 
diff --git a/src/tests/units/gob-test.r3 b/src/tests/units/gob-test.r3
index 8b3c03e87a..7bc4fdaca1 100644
--- a/src/tests/units/gob-test.r3
+++ b/src/tests/units/gob-test.r3
@@ -17,11 +17,13 @@ Rebol [
 		--assert 1   = index? back g
 		--assert 2   = index? next g
 		--assert 3   = index? tail g
+		--assert 2   = index? at g 2
 	--test-- "indexz? gob!"
 		--assert 0   = indexz? g
 		--assert 0   = indexz? back g
 		--assert 1   = indexz? next g
 		--assert 2   = indexz? tail g
+		--assert 1   = indexz? atz g 1
 ===end-group===
 
 ===start-group=== "gob issues"
diff --git a/src/tests/units/image-test.r3 b/src/tests/units/image-test.r3
index 8921f9a0ea..dcc80cad20 100644
--- a/src/tests/units/image-test.r3
+++ b/src/tests/units/image-test.r3
@@ -69,22 +69,55 @@ Rebol [
 
 ===end-group===
 
-===start-group=== "INDEX? / INDEXZ?"
+===start-group=== "INDEX? / INDEXZ? / AT / ATZ"
 	img: make image! 2x2
 	--test-- "index? image!"
-		--assert 1   = index? img
-		--assert 2   = index? next img
-		--assert 5   = index? tail img
+		--assert 1 = index? img
+		--assert 2 = index? next img
+		--assert 5 = index? tail img
+		--assert 4 = index? skip tail img -1
+	--test-- "index? at image!"
+		--assert 1 = index? at img -1
+		--assert 1 = index? at img 0
+		--assert 1 = index? at img 1
+		--assert 2 = index? at img 2
+		--assert 5 = index? at img 6
+		--assert 1 = index? skip at img 2 -1
+	--test-- "index?/xy image!"
 		--assert 1x1 = index?/xy img
 		--assert 2x1 = index?/xy next img
 		--assert 1x3 = index?/xy tail img
+		--assert 2x2 = index?/xy skip tail img -1
+	--test-- "index?/xy at image!"
+		--assert 1x1 = index?/xy at img 1x1
+		--assert 1x2 = index?/xy at img 1x2
+		--assert 2x2 = index?/xy at img 2x2
+		--assert 1x3 = index?/xy at img 20x2
+		--assert 1x2 = index?/xy skip at img 2x2 -1x0
 	--test-- "indexz? image!"
-		--assert 0   = indexz? img
-		--assert 1   = indexz? next img
-		--assert 4   = indexz? tail img
+		--assert 0 = indexz? img
+		--assert 1 = indexz? next img
+		--assert 4 = indexz? tail img
+		--assert 3 = indexz? skip tail img -1
+	--test-- "indexz? atz image!"
+		--assert 0 = indexz? atz img -1
+		--assert 0 = indexz? atz img 0
+		--assert 2 = indexz? atz img 2
+		--assert 4 = indexz? atz img 6
+		--assert 3 = indexz? skip atz img 6 -1
+		--assert 1 = indexz? skip atz img 2 -1
+	--test-- "indexz?/xy image!"
 		--assert 0x0 = indexz?/xy img
 		--assert 1x0 = indexz?/xy next img
 		--assert 0x2 = indexz?/xy tail img
+		--assert 1x1 = indexz?/xy skip tail img -1x0
+	--test-- "indexz?/xy atz image!"
+		--assert 0x0 = indexz?/xy atz img 0x0
+		--assert 0x1 = indexz?/xy atz img 0x1
+		--assert 1x1 = indexz?/xy atz img 1x1
+		--assert 0x2 = indexz?/xy atz img 2x2
+		--assert 0x2 = indexz?/xy atz img 20x2
+		--assert 0x1 = indexz?/xy skip atz img 1x1 -1x0
 ===end-group===
 
 ===start-group=== "FOREACH"
@@ -250,26 +283,26 @@ Rebol [
 000000000000FFFFFFFFFFFF
 FFFFFFFFFFFFFFFFFFFFFFFF
 FFFFFFFFFFFFFFFFFFFFFFFF}
-		change at img 1x1 make image! [2x2 220.22.22]
+		change at img 2x2 make image! [2x2 220.22.22]
 		--assert img/rgb = #{
 000000000000FFFFFFFFFFFF
 000000DC1616DC1616FFFFFF
 FFFFFFDC1616DC1616FFFFFF
 FFFFFFFFFFFFFFFFFFFFFFFF}
-		change at img 2x2 make image! [3x3 33.33.33]
+		change at img 3x3 make image! [3x3 33.33.33]
 		--assert img/rgb = #{
 000000000000FFFFFFFFFFFF
 000000DC1616DC1616FFFFFF
 FFFFFFDC1616212121212121
 FFFFFFFFFFFF212121212121}
-		change at img 0x3 make image! [4x4 66.166.66]
+		change at img 1x4 make image! [4x4 66.166.66]
 		--assert img/rgb = #{
 000000000000FFFFFFFFFFFF
 000000DC1616DC1616FFFFFF
 FFFFFFDC1616212121212121
 42A64242A64242A64242A642}
 
-		change at img 3x0 make image! [2x1 #{AAAAAABBBBBB}]
+		change at img 4x1 make image! [2x1 #{AAAAAABBBBBB}]
 		--assert img/rgb = #{
 000000000000FFFFFFAAAAAA
 000000DC1616DC1616FFFFFF
diff --git a/src/tests/units/series-test.r3 b/src/tests/units/series-test.r3
index 138636fe2a..b8a57e371c 100644
--- a/src/tests/units/series-test.r3
+++ b/src/tests/units/series-test.r3
@@ -627,6 +627,10 @@ Rebol [
 			0 = indexz? s
 			1 = indexz? next s
 			3 = indexz? tail s
+			0 = indexz? atz s -1
+			0 = indexz? atz s 0
+			2 = indexz? atz s 2
+			3 = indexz? atz s 6
 		]
 	--test-- "indexz? on binary"
 		s: to binary! "abc"
@@ -634,6 +638,10 @@ Rebol [
 			0 = indexz? s
 			1 = indexz? next s
 			3 = indexz? tail s
+			0 = indexz? atz s -1
+			0 = indexz? atz s 0
+			2 = indexz? atz s 2
+			3 = indexz? atz s 6
 		]
 	--test-- "indexz? on block"
 		s: [1 2 3]
@@ -641,6 +649,10 @@ Rebol [
 			0 = indexz? s
 			1 = indexz? next s
 			3 = indexz? tail s
+			0 = indexz? atz s -1
+			0 = indexz? atz s 0
+			2 = indexz? atz s 2
+			3 = indexz? atz s 6
 		]
 	--test-- "indexz? on vector"
 		s: #[u16! 3]
@@ -648,6 +660,10 @@ Rebol [
 			0 = indexz? s
 			1 = indexz? next s
 			3 = indexz? tail s
+			0 = indexz? atz s -1
+			0 = indexz? atz s 0
+			2 = indexz? atz s 2
+			3 = indexz? atz s 6
 		]
 ===end-group===