BUG #5533: PQexecParams in Binary Mode returns incorrect value for float4

The following bug has been logged online:

Bug reference: 5533
Logged by:
Email address: myk321(at)gmail(dot)com
PostgreSQL version: 8.4.3
Operating system: Ubuntu 10.04
Description: PQexecParams in Binary Mode returns incorrect value for
float4
Details:

Experience: PQexecParams (pqlib) in binary mode returns incorrect value for
float4 data type.

Example: Code below extracts a 0.75 float4 value from PostgreSQL, but
pqlib's PQexecParams returns 1.812500. Same query in text mode returns 0.75
correctly. Expected 0.75 return value in Binary mode.

Machine:
Dell Precision - Core 2 Duo
Ubuntu 10.04 LTS (Lucid Lynx)
PostgresQL 8.4.3 on i686-pc-linux-gnu, compiled by GCC gcc (GCC) 3.4.6
20060404 (Red Hat 3.4.6-10), 32-bit

Demo.c starts here
// C Prototypes and Std Include headers
#include <ftw.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include "libpq-fe.h"

// Some silly parameters for handling postgreql
#define oidINT4 23;
#define oidFLOAT4 700;

#define TextFormat 0;
#define BinaryFormat 1;

void main()
{
PGconn* conn;
PGresult *res;

//Parameters for the insert
int inParams = 2;
Oid iParamTypes[2];
char* iParamValues[2];
int iParamLengths[2];
int iParamFormats[2];
int iResultFormat = BinaryFormat;

//Parameters for the select
int snParams = 1;
Oid sParamTypes[1];
char* sParamValues[1];
int sParamLengths[1];
int sParamFormats[1];
int sResultFormat = BinaryFormat;

//Index Value
int Index;

//Variables to handle the float4
union
{
float f;
unsigned int i;
} Swap;
char* ptrFltValue;

// Connect to the default database and create a test table consisting of a
column of int4 and float4
conn = PQconnectdb("dbname=postgres user=postgres password=<insert password
here>");
res = PQexec(conn, "CREATE TABLE testtbl( Intgr int4, Flt float8, PRIMARY
KEY ( Intgr ));");
PQclear(res);

//Insert 1 rows, 1 containing 0.75 the float4 field (100 in the int4
field)
iParamTypes[0] = oidINT4;
iParamTypes[1] = oidFLOAT4;
iParamLengths[0] = sizeof(unsigned int);
iParamLengths[1] = sizeof(float);
iParamFormats[0] = BinaryFormat;
iParamFormats[1] = BinaryFormat;
Index = htonl(100);
iParamValues[0] = (char*) &Index;
Swap.f = 0.75;
Swap.i = htonl(Swap.i);
iParamValues[1] = (char*) &Swap;
res = PQexecParams(conn, "Insert into testtbl(Intgr, Flt) Values ($1,
$2);", inParams, &iParamTypes,
iParamValues, &iParamLengths, &iParamFormats, iResultFormat);
PQclear(res);

//Retrieve the row in Binary mode
sParamTypes[0] = oidINT4;
sParamLengths[0] = sizeof(unsigned int);
sParamFormats[0] = BinaryFormat;
sParamValues[0] = (char*) &Index;
res = PQexecParams(conn, "SELECT * FROM testtbl where (Intgr = $1);",
snParams, &sParamTypes,
sParamValues, &sParamLengths, &sParamFormats, sResultFormat);
ptrFltValue = PQgetvalue(res,0,1);
Swap.i = ntohl(*((int *) ptrFltValue));

//Print the Binary mode result
printf("Flt retrieved in Binary mode is = %f.\n", Swap.f);

//Retrieve the row in Text mode
PQclear(res);
sResultFormat = TextFormat;
res = PQexecParams(conn, "SELECT * FROM testtbl where (Intgr = $1);",
snParams, &sParamTypes,
sParamValues, &sParamLengths, &sParamFormats, sResultFormat);

//Print the Text mode results
printf("Flt retrieved in Binary mode is = %s.\n", PQgetvalue(res,0,1));

//Clean-up
PQclear(res);
PQfinish(conn);

return;
}

Demo.c ends here

Makefile starts here
#
# Makefile for Demo application
# Use by invoking 'make' on the command line
#
# Specify the compiler
CC = gcc

# Specify the pre-processor flags
CPPFLAGS += -I/opt/PostgreSQL/8.4/include
CPPFLAGS += -I${HOME}

# Specify the compiler flags
CFLAGS += -c
CFLAGS += -g

# Specify the linker flags
LDFLAGS += -g

# Specify the linker libraries
LDLIBS += -L/opt/PostgreSQL/8.4/lib -lpq
LDLIBS += /opt/PostgreSQL/8.4/lib/libssl.so.4
LDLIBS += /opt/PostgreSQL/8.4/lib/libcrypto.so.4

# Specify the files making up the application
SOURCES = Demo.c
EXECUTABLE = Demo

all: $(EXECUTABLE)

$(EXECUTABLE): $(OBJECTS)
$(CC) $(LDFLAGS) $(LDLIBS) $(OBJECTS) -o $@

.c.o:
$(CC) $(CPPFLAGS) $(CFLAGS) $< -o $@

install:
@echo "Build complete!"

Makefile ends here

Some needless speculation:
0.75 = 3F400000 (as IEEE 32-bit float)
0.75 = 3FE8000000000000 (as IEEE 64-bit float)
1.812500 = 3FE80000 (as returned by PQexecParams)
i.e. the return value is the first 32-bits of the 64-bit representation of
the correct value.

Same result apparent for 1.22 test value
Returns: 1.902500.
1.22 = 3F9C28F6 (as IEEE 32-bit float)
1.22 = 3FF3851EB851EB85 (as 64-bit IEEE 64-bit float)
1.9025 = 3FF3851E (as returned by PQexecParams)
Ref: http://babbage.cs.qc.cuny.edu/IEEE-754/Decimal.html