Differences

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--- sd:isa [2026/06/16 12:34] – appledog
+++ sd:isa [2026/06/18 04:53] (current) – appledog
@@ Line 178: / Line 178: @@
 === Tier 4: Acceleration (LLVM / Forth / Hardware)
-Instructions added to remove work from a specific hot path rather than to add
+Instructions added to remove work from a specific hot path rather than to add expressiveness. Each one has a primary consumer noted below.
-expressiveness. Each one has a primary consumer noted below.
+Canidates for inclusion: LEA, fused CMP-Bcc and CMP-Jcc, conditional move, LD_IDX16
 | #   | hex  | Mnemonic | Example          | Description                                  | Consumer | Flags |
@@ Line 388: / Line 389: @@
 <wrap #cmpc />
 **''#142 $8E CMPC ELM, FLD, C''** (alias //CMPC3//)\\
-Non-zero byte compare, useful for strings. Compares up to C characters; C returns
+Non-zero byte compare, useful for strings. Compares up to C characters; C returns either the index of the first mismatch or the matched length. Sets ZERO on a full match; otherwise CARRY distinguishes the -1 / +1 ordering.
-either the index of the first mismatch or the matched length. Sets ZERO on a full
-match; otherwise CARRY distinguishes the -1 / +1 ordering.
-CMPC allows early termination when ''byte_a == 0'' -- the C-string "begins with"
+CMPC allows early termination when ''byte_a == 0'' -- the C-string "begins with" semantics. If both strings reach a terminator at the same position with all prior bytes equal, the loop exits matched (Z=1, C=1). Only ''byte_a'' is tested because by that point ''byte_a == byte_b'' is already proven, so ''byte_a == 0'' implies ''byte_b == 0''. This lets CMPC do double duty: fixed-length compare and null-terminated strcmp in one instruction.
-semantics. If both strings reach a terminator at the same position with all prior
-bytes equal, the loop exits matched (Z=1, C=1). Only ''byte_a'' is tested because by
-that point ''byte_a == byte_b`` is already proven, so ''byte_a == 0'' implies
-''byte_b == 0''. This lets CMPC do double duty: fixed-length compare and
-null-terminated strcmp in one instruction.
 <wrap #skpc />
@@ Line 523: / Line 517: @@
 <codify armasm>
-    LDFLX $F000       ; loop start
+    LDFLX $F000       ; 8 byte loop data start
-    LDA #1
+    LDA #1            ; start at 1
-    STA [FLX]
+    STA [FLX]         ; write starting counter at first four bytes
-    LDA #1000
+    LDA #1000         ; go until 1000
-    STA [FLX+4]
+    STA [FLX+4]       ; write finish (until) counter at second four bytes
 loop:
-    LSTEPM
+    LSTEPM            ; INC N1, if N1==N2 set Z=1
     JNZ @loop
 </codify>
-Unlike a DEC loop it counts upward and supports an arbitrary start. It is a kludge
+Unlike a DEC loop it counts upward and supports an arbitrary start. The generalized form of this is [[#lstep|LSTEP]] which counts downwards instead.
-for Forth and has been generalized by [[#lstep|LSTEP]]; once Forth uses LSTEP,
-LSTEPM is a candidate for removal.
+Only used by Forth. It is recommended to use LSTEP instead; this instruction is a canidate for removal.
 <wrap #ttos />