Add engineering output mode

Similar to scientific mode, engineering mode also displays numbers in
base 10 exponential notation, with the difference that exponents are
always multiples of 3, to facilitate the interpretation in terms of
SI prefixes.

The mode is activated in config thru "engineering" or "eng. For base
and base2, it uses the special value 1000.

config.c

@@ -274,6 +274,8 @@ STATIC NAMETYPE modes[] = {
 	{"scientific",	MODE_EXP},
 	{"sci",		MODE_EXP},
 	{"exp",		MODE_EXP},
+	{"engineering",	MODE_ENG},
+	{"eng",		MODE_ENG},
 	{"hexadecimal", MODE_HEX},
 	{"hex",		MODE_HEX},
 	{"octal",	MODE_OCTAL},

file.c

@@ -1048,6 +1048,9 @@ idprintf(FILEID id, char *fmt, int count, VALUE **vals)
 		case 'e':
 			newmode = MODE_EXP;
 			break;
+		case 'n':
+			newmode = MODE_ENG;
+			break;
 		case 'g':
 			newmode = MODE_REAL_AUTO;
 			break;

func.c

@@ -7839,6 +7839,9 @@ f_base(int count, NUMBER **vals)
 	case 16:
 		oldbase = math_setmode(MODE_HEX);
 		break;
+        case 1000:
+		oldbase = math_setmode(MODE_ENG);
+		break;
 	default:
 		math_error("Unsupported base");
 		/*NOTREACHED*/
@@ -7893,6 +7896,9 @@ f_base2(int count, NUMBER **vals)
 	case 16:
 		oldbase = math_setmode2(MODE_HEX);
 		break;
+        case 1000:
+		oldbase = math_setmode(MODE_ENG);
+		break;
 	default:
 		math_error("Unsupported base");
 		/*NOTREACHED*/
@@ -7933,6 +7939,9 @@ base_value(long mode, int defval)
 			result = qalloc();
 			ztenpow(20, &result->num);
 			break;
+		case MODE_ENG:
+			result = itoq(1000);
+			break;
 		case MODE_HEX:
 			result = itoq(16);
 			break;
@@ -7964,6 +7973,9 @@ base_value(long mode, int defval)
 		result = qalloc();
 		ztenpow(20, &result->num);
 		break;
+	case MODE_ENG:
+		result = itoq(1000);
+		break;
 	case MODE_HEX:
 		result = itoq(16);
 		break;

help/base

@@ -44,6 +44,9 @@ DESCRIPTION
 			"sci"
 			"exp"
 
+	    1000	"engineering"	base 10 notation with exponent
+			"eng"		multiple of 3
+
     For convenience, any non-integer value is assumed to mean base 10
     fractions and any integer >= 2^64 is assumed to mean base 10
     scientific notation.
@@ -76,7 +79,7 @@ LINK LIBRARY
     int math_setmode(int newmode)
 
     NOTE: newmode must be one of MODE_DEFAULT, MODE_FRAC, MODE_INT,
-	  MODE_REAL, MODE_EXP, MODE_HEX, MODE_OCTAL, MODE_BINARY
+	  MODE_REAL, MODE_EXP, MODE_ENG, MODE_HEX, MODE_OCTAL, MODE_BINARY
 
 SEE ALSO
     base2, config, str

help/base2

@@ -50,6 +50,9 @@ DESCRIPTION
 			"sci"
 			"exp"
 
+	    1000	"engineering"	base 10 notation with exponent
+			"eng"		multiple of 3
+
 	       0	"off"		disable double base output
 
     For convenience, any non-integer non-zero value is assumed to mean
@@ -87,7 +90,7 @@ LINK LIBRARY
     int math_setmode2(int newmode)
 
     NOTE: newmode must be one of MODE_DEFAULT, MODE_FRAC, MODE_INT,
-	  MODE_REAL, MODE_EXP, MODE_HEX, MODE_OCTAL, MODE_BINARY,
+	  MODE_REAL, MODE_EXP, MODE_ENG, MODE_HEX, MODE_OCTAL, MODE_BINARY,
 	  MODE2_OFF
 
 SEE ALSO

help/config

@@ -165,8 +165,8 @@ DESCRIPTION
     config("display", int)
 
     The "display" parameter specifies the maximum number of digits after
-    the decimal point to be printed in real or exponential mode in
+    the decimal point to be printed in real, exponential or engineering
-    normal unformatted printing (print, strprint, fprint) or in
+    mode in normal unformatted printing (print, strprint, fprint) or in
     formatted printing (printf, strprintf, fprintf) when precision is not
     specified.	The initial value for oldstd is 20, for newstd 10.
     The parameter may be changed to the value d by either
@@ -234,6 +234,9 @@ DESCRIPTION
 	    "sci"
 	    "exp"
 
+	    "engineering"	base 10 notation with exponent	base(10e6)
+	    "eng"		multiple of 3
+
     Where multiple strings are given, the first string listed is what
     config("mode") will return.
 

qio.c

@@ -247,6 +247,37 @@ qprintnum(NUMBER *q, int outmode, LEN outdigits)
 		PRINTF1("e%ld", exp);
 		break;
 
+    case MODE_ENG:
+		if (qiszero(q)) {
+			PUTCHAR('0');
+			return;
+		}
+		tmpval = *q;
+		tmpval.num.sign = 0;
+		exp = qilog10(&tmpval);
+		if (exp == 0) {		/* in range to output as real */
+			qprintnum(q, MODE_REAL, outdigits);
+			return;
+		}
+		tmpval.num = _one_;
+		tmpval.den = _one_;
+		if (exp > 0) {
+            exp -= exp % 3;
+			ztenpow(exp, &tmpval.den);
+        } else {
+            long remainder = exp % 3;
+            if (remainder)
+                exp -= remainder + 3;
+			ztenpow(-exp, &tmpval.num);
+        }
+		q = qmul(q, &tmpval);
+		zfree(tmpval.num);
+		zfree(tmpval.den);
+		qprintnum(q, MODE_REAL, outdigits);
+		qfree(q);
+		PRINTF1("e%ld", exp);
+        break;
+
 	case MODE_REAL_AUTO:
 	{
 		const int P = conf->outdigits ? conf->outdigits : 1;

zmath.h

@@ -594,7 +594,8 @@ E_FUNC void zredcpower(REDC *rp, ZVALUE z1, ZVALUE z2, ZVALUE *res);
 #define MODE_OCTAL	6
 #define MODE_BINARY	7
 #define MODE_REAL_AUTO	8
-#define MODE_MAX	8
+#define MODE_ENG    9
+#define MODE_MAX	9
 #define MODE2_OFF	(MODE_MAX+1)
 
 /* XXX - perhaps we need the MODE_REAL_AUTO vs MODE_REAL as a config mode? */