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| author | Sven Eisenhauer <sven@sven-eisenhauer.net> | 2023-11-10 15:11:48 +0100 |
|---|---|---|
| committer | Sven Eisenhauer <sven@sven-eisenhauer.net> | 2023-11-10 15:11:48 +0100 |
| commit | 33613a85afc4b1481367fbe92a17ee59c240250b (patch) | |
| tree | 670b842326116b376b505ec2263878912fca97e2 /Bachelor/Mikroprozessorsysteme2/ARM202U/EXAMPLES/EXPLASM/UTOA1.S | |
| download | Studium-33613a85afc4b1481367fbe92a17ee59c240250b.tar.gz Studium-33613a85afc4b1481367fbe92a17ee59c240250b.tar.bz2 | |
Diffstat (limited to 'Bachelor/Mikroprozessorsysteme2/ARM202U/EXAMPLES/EXPLASM/UTOA1.S')
| -rw-r--r-- | Bachelor/Mikroprozessorsysteme2/ARM202U/EXAMPLES/EXPLASM/UTOA1.S | 60 |
1 files changed, 60 insertions, 0 deletions
diff --git a/Bachelor/Mikroprozessorsysteme2/ARM202U/EXAMPLES/EXPLASM/UTOA1.S b/Bachelor/Mikroprozessorsysteme2/ARM202U/EXAMPLES/EXPLASM/UTOA1.S new file mode 100644 index 0000000..369773a --- /dev/null +++ b/Bachelor/Mikroprozessorsysteme2/ARM202U/EXAMPLES/EXPLASM/UTOA1.S @@ -0,0 +1,60 @@ +; This demonstrates recursion in ARM assembler.
+; this version does not perform stack checking.
+;
+; Converting a number to a string can be expressed using a divide-and-
+; conquer algorithm:
+; <string> = "<number/10><number%10>"
+
+ AREA |utoa$$code|, CODE, READONLY
+
+ EXPORT dtoa
+ EXPORT utoa
+
+ IMPORT udiv10
+
+dtoa
+; converts signed word to string
+; a1 = char *buffer
+; a2 = signed int number
+; on exit:
+; a1 = char *end_of_string
+
+ CMP a2, #0
+ RSBMI a2, a2, #0; make a2 positive
+ MOVMI ip, #'-'
+ STRMIB ip, [ a1 ], #1 ; add minus sign to buffer
+
+; *** intentional drop-through to utoa ***
+
+utoa
+; recursive routine to convert unsigned word to string
+; on entry:
+; a1 = char *buffer
+; a2 = unsigned int number
+; on exit:
+; a1 = char *end_of_string ; character after last digit
+; all other registers preserved
+
+ STMFD sp!, {v1, v2, lr} ; save 2 variable registers and
+ ; the return address
+
+ MOV v1, a1 ; keep char *buffer for later
+ MOV v2, a2 ; and keep the number for later
+ MOV a1, a2
+ BL udiv10 ; on return, the quotient is in a1
+
+ SUB v2, v2, a1, LSL #3 ; number - 8*quoitient
+ SUB v2, v2, a1, LSL #1 ; - 2*quotient = remainder
+
+ CMP a1, #0 ; quotient non-zero?
+ MOVNE a2, a1 ; quotient to a2...
+ MOV a1, v1 ; buffer pointer unconditionally to a1
+ BLNE utoa ; conditional recursive call to utoa
+
+ ADD v2, v2, #'0' ; final digit
+ STRB v2, [a1], #1 ; store digit at end of buffer
+
+ LDMFD sp!, {v1, v2, pc} ; restore and return
+
+ END
+
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